The term "Third World" arose during the Cold War and it was used to define countries that remained non-aligned with either NATO or the Warsaw Pact. The United States, Canada, Japan, South Korea, Western European nations and their allies represented the "First World", while the Soviet Union, China, Cuba, North Korea, Vietnam and their allies represented the "Second World". This terminology provided a way of broadly categorizing the nations of the Earth into three groups based on political divisions. Due to the complex history of evolving meanings and contexts, there is no clear or agreed-upon definition of the Third World.  Strictly speaking, "Third World" was a political, rather than an economic, grouping. 
Because many Third World countries were economically poor and non-industrialized, it became a stereotype to refer to developing countries as "third world countries", yet the "Third World" term is also often taken to include newly industrialized countries like Brazil, China and India now more commonly referred to as part of BRIC. Some countries in the Eastern Bloc, such as Cuba, were often regarded as "Third World". The Third World was normally seen to include many countries with colonial pasts in Africa, Latin America, Oceania, and Asia. It was also sometimes taken as synonymous with countries in the Non-Aligned Movement. In the dependency theory of thinkers like Raúl Prebisch, Walter Rodney, Theotônio dos Santos, and Andre Gunder Frank, the Third World has also been connected to the world-systemic economic division as "periphery" countries dominated by the countries comprising the economic "core". 
Since the dissolution of the Soviet Union and the end of the Cold War, the term Third World has decreased in use. It is being replaced with terms such as developing countries, least developed countries or the Global South. The concept itself has become outdated as it no longer represents the current political or economic state of the world and as historically poor countries have transited different income stages. In the Cold War, some European democracies (Austria, Finland, Republic of Ireland, Sweden, and Switzerland) were neutral in the sense of not joining NATO, but were prosperous, never joined the Non-Aligned Movement, and seldom self-identified as part of the Third World.
French demographer, anthropologist, and historian Alfred Sauvy, in an article published in the French magazine L'Observateur , August 14, 1952, coined the term third world (tiers monde), referring to countries that were playing a small role in international trade and business.  His usage was a reference to the Third Estate (tiers état), the commoners of France who, before and during the French Revolution, opposed the clergy and nobles, who composed the First Estate and Second Estate, respectively (hence the use of the older form tiers rather than the modern troisième for "third"). Sauvy wrote, "This third world ignored, exploited, despised like the third estate also wants to be something."  In the context of the Cold War, he conveyed the concept of political non-alignment with either the capitalist or communist bloc.  Simplistic interpretations quickly led to the term merely designating these unaligned countries. 
The "Three Worlds Theory" developed by Mao Zedong is different from the Western theory of the Three Worlds or Third World. For example, in the Western theory, China and India belong respectively to the second and third worlds, but in Mao's theory both China and India are part of the Third World which he defined as consisting of exploited nations.
Third Worldism is a political movement that argues for the unity of third-world nations against first-world influence and the principle of non-interference in other countries' domestic affairs. Groups most notable for expressing and exercising this idea are the Non-Aligned Movement (NAM) and the Group of 77 which provide a base for relations and diplomacy between not just the third-world countries, but between the third-world and the first and second worlds. The notion has been criticized as providing a fig leaf for human rights violations and political repression by dictatorships. 
Since 1990, this term has been redefined to make it more correct politically. Initially, the term “third world” meant that a nation is “under-developed”.  However, today it is replaced by the term “developing".
Many times there is a clear distinction between First and Third Worlds. When talking about the Global North and the Global South, the majority of the time the two go hand in hand. People refer to the two as "Third World/South" and "First World/North" because the Global North is more affluent and developed, whereas the Global South is less developed and often poorer. 
To counter this mode of thought, some scholars began proposing the idea of a change in world dynamics that began in the late 1980s, and termed it the Great Convergence.  As Jack A. Goldstone and his colleagues put it, "in the twentieth century, the Great Divergence peaked before the First World War and continued until the early 1970s, then, after two decades of indeterminate fluctuations, in the late 1980s, it was replaced by the Great Convergence as the majority of Third World countries reached economic growth rates significantly higher than those in most First World countries". 
Others have observed a return to Cold War-era alignments (MacKinnon, 2007; Lucas, 2008), this time with substantial changes between 1990–2015 in geography, the world economy and relationship dynamics between current and emerging world powers; not necessarily redefining the classic meaning of First, Second, and Third World terms, but rather which countries belong to them by way of association to which world power or coalition of countries — such as G7, the European Union, OECD; G20, OPEC, N-11, BRICS, ASEAN; the African Union, and the Eurasian Union.
Most Third World countries are former colonies. Having gained independence, many of these countries, especially smaller ones, were faced with the challenges of nation- and institution-building on their own for the first time. Due to this common background, many of these nations were "developing" in economic terms for most of the 20th century, and many still are. This term, used today, generally denotes countries that have not developed to the same levels as OECD countries, and are thus in the process of developing.
In the 1980s, economist Peter Bauer offered a competing definition for the term "Third World". He claimed that the attachment of Third World status to a particular country was not based on any stable economic or political criteria, and was a mostly arbitrary process. The large diversity of countries considered part of the Third World — from Indonesia to Afghanistan — ranged widely from economically primitive to economically advanced and from politically non-aligned to Soviet- or Western-leaning. An argument could also be made for how parts of the U.S. are more like the Third World. 
The only characteristic that Bauer found common in all Third World countries was that their governments "demand and receive Western aid," the giving of which he strongly opposed. Thus, the aggregate term "Third World" was challenged as misleading even during the Cold War period, because it had no consistent or collective identity among the countries it supposedly encompassed.
During the Cold War, unaligned countries of the Third World  were seen as potential allies by both the First and Second World. Therefore, the United States and the Soviet Union went to great lengths to establish connections in these countries by offering economic and military support to gain strategically located alliances (e.g., the United States in Vietnam or the Soviet Union in Cuba).  By the end of the Cold War, many Third World countries had adopted capitalist or communist economic models and continued to receive support from the side they had chosen. Throughout the Cold War and beyond, the countries of the Third World have been the priority recipients of Western foreign aid and the focus of economic development through mainstream theories such as modernization theory and dependency theory. 
By the end of the 1960s, the idea of the Third World came to represent countries in Africa, Asia, and Latin America that were considered underdeveloped by the West based on a variety of characteristics (low economic development, low life expectancy, high rates of poverty and disease, etc.).  These countries became the targets for aid and support from governments, NGOs and individuals from wealthier nations. One popular model, known as Rostow's stages of growth, argued that development took place in 5 stages (Traditional Society; Pre-conditions for Take-off; Take-off; Drive to Maturity; Age of High Mass Consumption).  W. W. Rostow argued that Take-off was the critical stage that the Third World was missing or struggling with. Thus, foreign aid was needed to help kick-start industrialization and economic growth in these countries. 
Since 1990 the term "Third World" has been redefined in many evolving dictionaries in several languages to refer to countries considered to be underdeveloped economically and/or socially. From a "political correctness" standpoint the term "Third World" may be considered outdated, which its concept is mostly a historical term and cannot fully address what means by developing and less-developed countries today. Around the early 1960s, the term "underdeveloped countries" occurred and the Third World serves to be its synonym, but after it has been officially used by politicians, 'underdeveloped countries' is soon been replaced by 'developing' and 'less-developed countries,' because the prior one shows hostility and disrespect, in which the Third World is often characterized with stereotypes.  The whole 'Four Worlds' system of classification has also been described as derogatory because the standard mainly focused on each nations' Gross National Product. 
The general definition of the Third World can be traced back to the history that nations positioned as neutral and independent during the Cold War were considered as Third World Countries, and normally these countries are defined by high poverty rates, lack of resources, and unstable financial standing.  However, based on the rapid development of modernization and globalization, countries that were used to be considered as Third World countries achieve big economic growth, such as Brazil, India, and Indonesia, which can no longer be defined by poor economic status or low GNP today. The differences among nations of the Third World are continually growing throughout time, and it will be hard to use the Third World to define and organize groups of nations based on their common political arrangements since most countries live under diverse creeds in this era, such as Mexico, El Salvador, and Singapore, which they all have their own political system.  The Third World categorization becomes anachronistic since its political classification and economic system are distinct to be applied in today's society. Based on the Third World standards, any region of the world can be categorized into any of the four types of relationships among state and society, and will eventually end in four outcomes: praetorianism, multi-authority, quasi-democratic and viable democracy.  However, political culture is never going to be limited by the rule and the concept of the Third World can be circumscribed.
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreement on which countries fit this category. The term low and middle-income country (LMIC) is often used interchangeably but refers only to the economy of the countries. The World Bank classifies the world's economies into four groups, based on gross national income per capita: high, upper-middle, lower-middle, and low income countries. Least developed countries, landlocked developing countries and small island developing states are all sub-groupings of developing countries. Countries on the other end of the spectrum are usually referred to as high-income countries or developed countries.
International relations (IR) are the interactions among sovereign states. The scientific study of those interactions is called international studies, or international affairs. In a broader sense, it concerns all activities between states—such as war, diplomacy, trade, and foreign policy—as well as relations with and among other international actors, such as intergovernmental organisations (IGOs), international nongovernmental organisations (INGOs), international legal bodies, and multinational corporations (MNCs). There are several schools of thought within IR, of which the most prominent are realism, liberalism, and constructivism.
The concept of First World originated during the Cold War and comprised countries that were under the influence of the United States and the rest of NATO and opposed the Soviet Union and/or communism during the Cold War. Since the collapse of the Soviet Union in 1991, the definition has instead largely shifted to any country with little political risk and a well-functioning democracy, rule of law, capitalist economy, economic stability, and high standard of living. Various ways in which modern First World countries are usually determined include GDP, GNP, literacy rates, life expectancy, and the Human Development Index. In common usage, "first world" typically refers to "the highly developed industrialized nations often considered the westernized countries of the world".
The Second World is a term originating during the Cold War for the industrial socialist states that were under the influence of the Soviet Union. In the first two decades following World War II, 19 communist states emerged; all of these were at least originally within the Soviet sphere of influence, though some broke with Moscow and developed their own path of socialism while retaining Communist governments. Most communist states remained part of the Eastern Bloc until the dissolution of the Soviet Union in 1991; afterwards, only five communist states remained: China, Cuba, Laos, North Korea, and Vietnam. Along with "First World" and "Third World", the term was used to divide the states of Earth into three broad categories.
Neocolonialism is the continuation or reimposition of imperialist rule by a state over another nominally independent state. Neocolonialism takes the form of economic imperialism, globalization, cultural imperialism and conditional aid to influence or control a developing country instead of the previous colonial methods of direct military control or indirect political control (hegemony).
The concept of Global North and Global South is used to describe a grouping of countries along the lines of socio-economic and political characteristics. The Global South is a term generally used to identify countries and regions in the regions of Latin America, Africa, Asia and Oceania. Most of humanity resides in the Global South. Many countries in the Global South are characterized by low-income, dense population, poor infrastructure, often political or cultural marginalization, and are on one side of the divide; while on the other side is the Global North. As such, the terms Global North and Global South do not refer to the directional North-south as many of the Global South countries are geographically located in the Northern Hemisphere.
International development or global development is a broad concept denoting the idea that societies and countries have differing levels of economic or human development on an international scale. It is the basis for international classifications such as developed country, developing country and least developed country, and for a field of practice and research that in various ways engages with international development processes. There are, however, many schools of thought and conventions regarding which are the exact features constituting the "development" of a country.
Dependency theory is the idea that resources flow from a "periphery" of poor and underdeveloped states to a "core" of wealthy states, enriching the latter at the expense of the former. A central contention of dependency theory is that poor states are impoverished and rich ones enriched by the way poor states are integrated into the "world system". This theory was officially developed in the late 1960s following World War II, as scholars searched for the root issue in the lack of development in Latin America.
Underdevelopment, in the context of international development, reflects a broad condition or phenomena defined and critiqued by theorists in fields such as economics, development studies, and postcolonial studies. Used primarily to distinguish states along benchmarks concerning human development—such as macro-economic growth, health, education, and standards of living—an "underdeveloped" state is framed as the antithesis of a "developed", modern, or industrialized state. Popularized, dominant images of underdeveloped states include those that have less stable economies, less democratic political regimes, greater poverty, malnutrition, and poorer public health and education systems.
Modernization theory is used to explain the process of modernization within societies. The "classical" theories of modernization of the 1950s and 1960s drew on sociological analyses of Karl Marx, Emile Durkheim and a partial reading of Max Weber, and were strongly influenced by the writings of Harvard sociologist Talcott Parsons. Modernization theory was a dominant paradigm in the social sciences in the 1950s and 1960s, then went into a deep eclipse. It made a comeback after 1991, when Francis Fukuyama wrote about the end of the Cold War as confirmation on modernization theory and more generally of universal history. But the theory remains a controversial model.
World-systems theory is a multidisciplinary approach to world history and social change which emphasizes the world-system as the primary unit of social analysis.
Development theory is a collection of theories about how desirable change in society is best achieved. Such theories draw on a variety of social science disciplines and approaches. In this article, multiple theories are discussed, as are recent developments with regard to these theories. Depending on which theory that is being looked at, there are different explanations to the process of development and their inequalities.
The flying geese paradigm is a view of Japanese scholars regarding technological development in Southeast Asia which sees Japan as a leading power. It was developed in the 1930s, but gained wider popularity in the 1960s, after its author, Kaname Akamatsu, published his ideas in the Journal of Developing Economies.
Third-Worldism is a political concept and ideology that emerged in the late 1940s or early 1950s during the Cold War and tried to generate unity among the nations that did not want to take sides between the United States and the Soviet Union. The concept is closely related but not identical to the political theory of Maoism–Third Worldism.
In the field of international relations, the Three Worlds Theory by Mao Zedong proposed to the visiting Algerian President Houari Boumédiène in February 1974 that the international system operated as three contradictory politico-economic worlds. On April 10, 1974, at the 6th Special Session United Nations General Assembly, Vice-Premier Deng Xiaoping applied the Three Worlds Theory during the New International Economic Order presentations about the problems of raw materials and development, to explain the PRC's economic co-operation with non-communist countries.
Developmentalism is an economic theory which states that the best way for less developed economies to develop is through fostering a strong and varied internal market and imposing high tariffs on imported goods.
The anthropology of development is a term applied to a body of anthropological work which views development from a critical perspective. The kind of issues addressed, and implications for the approach typically adopted can be gleaned from a list questions posed by Gow (1996). These questions involve anthropologists asking why, if a key development goal is to alleviate poverty, is poverty increasing? Why is there such a gap between plans and outcomes? Why are those working in development so willing to disregard history and the lessons it might offer? Why is development so externally driven rather than having an internal basis? In short, why is there such a lack of planned development?
Maoism–Third Worldism (MTW) is a broad tendency which is mainly concerned with the infusion and synthesis of Marxism—particularly of the Marxist–Leninist–Maoist persuasion—with concepts of non-Marxist Third Worldism, namely dependency theory and world-systems theory.
The terms First World, Second World, and Third World were originally used to divide the world's nations into three categories. The complete overthrow of the pre–World War II status quo left two superpowers vying for ultimate global supremacy, a struggle known as the Cold War. They created two camps, known as blocs. These blocs formed the basis of the concepts of the First and Second Worlds. The Third World consisted of those countries that were not closely aligned with either bloc.
The Non-Aligned Movement (NAM) is a forum of 120 countries that are not formally aligned with or against any major power bloc. After the United Nations, it is the largest grouping of states worldwide.