Modernization theory is a description and explanation of the processes of transformation from traditional or underdeveloped societies to modern societies. In the words of one of the major proponents, "Historically, modernization is the process of change towards those types of social, economic, and political systems that have developed in Western Europe and North America from the seventeenth century to the nineteenth and have then spread to other European countries and in the nineteenth and twentieth centuries to the South American, Asian, and African continents
Modernization theory has been one of the major perspectives in the sociology of national development and underdevelopment since the 1950s.Many thinkers wrote about the modernization theory such as David Harrison,Rostow and Daniel lerner.One of the key thinkers in twentieth century Development Studies was W.W. Rostow, an American economist and government official. Prior to Rostow, approaches to development had been based on the assumption that "modernization" was characterized by the Western world (wealthier, more powerful countries at the time), which were able to advance from the initial stages of underdevelopment. Accordingly, other countries should model themselves after the West, aspiring to a "modern" state of capitalism and a liberal democracy. Using these ideas, Rostow penned his classicStages of Economic Growth in 1960, which presented five steps through which all countries must pass to become developed: 1) traditional society, 2) preconditions to take-off, 3) take-off, 4) drive to maturity, and 5) age of high mass consumption. The model asserted that all countries exist somewhere on this linear spectrum, and climb upward through each stage in the development process:
Traditional Society: This stage is characterized by a subsistent, agricultural based economy, with intensive labor and low levels of trading, and a population that does not have a scientific perspective on the world and technology.
Preconditions to Take-off: Here, a society begins to develop manufacturing, and a more national/international, as opposed to regional, outlook.
Take-off: Rostow describes this stage as a short period of intensive growth, in which industrialization begins to occur, and workers and institutions become concentrated around a new industry.
Drive to Maturity: This stage takes place over a long period of time, as standards of living rise, use of technology increases, and the national economy grows and diversifies.
Age of High Mass Consumption: At the time of writing, Rostow believed that Western countries, most notably the United States, occupied this last "developed" stage. Here, a country's economy flourishes in a capitalist system, characterized by mass production and consumerism.
Dependency theorists sharply critique the modernisation school. The earliest formulation of dependency theory came up alongside modernisation theory. The theory emerged first in Latin America , amongst social scientists such as Raul Prebisch, an Argentinian economist. The ideas of dependency were also developed, amongst others, by other Latin American social scientists such as Celso Furtado, Theotonio Dos Santos and F H Cardoso; by Samir Amin , by Andre Gunder Frank of Germany and by Paul Baran and Immanuel Wallerstein (who later formulated another, related version, called world-systems theory) of the US.

Dependency is also not a homogeneous, unified theory—serious analytical differences persist within the school. But in essence, dependency theory argues that the origins of persistent global poverty cannot be understood without reference to the entire international economic system. Underdevelopment is not a condition: it is an active process of impoverishment linked to development. That is, some parts of the world are underdeveloped because others are developed. They are not separate processes but two aspects of the same process.
In other words, economic growth in advanced countries created Third World poverty in its wake: not simply that the Third World is poor in comparison with the industrialised world; rather that it is poor because development of the industrial system in Western Europe and North America changed and impoverished many societies of Asia, Africa and Latin America, through colonialism, imperialism and extractive terms of trade.