Decolonization is the process by which a colony gains its independence from a colonial power, a process opposite to colonization. Decolonization could be achieved by attaining independence, integrating with the administering power or another state, or establishing a "free association" status. The UN has stated that in the process of decolonization there is no alternative to the principle of self-determination. Decolonization may involve peaceful negotiation and/or violent revolt by the native population. Decolonization in the strict sense is distinct from the break-up of traditional empires, and in modern academic discourse the period of decolonization generally refers to two major waves of independence from European colonial rule:

There appears to be some debate over whether the United States was decolonized after it gained independence, however this could just be rhetoric from those who do not view it as a legitimate nation.

In the 20th and 21st centuries "decolonization" usually refers to the achievement of independence by the various European colonies and protectorates in Asia and Africa following World War II. This conforms with an intellectual movement known as Post-Colonialism. A particularly active period of decolonization occurred between 1945 to 1960, beginning with the independence of Pakistan and India from Britain in 1947.

Source: http://en.wikipedia.org/wiki/Decolonisation