Discuss the factors that contributed to decolonization in the 20th century? What are the global ramifications of it?

One major factor that led to de-colonization was World War II. This was especially true in Southeast Asia and the Pacific, where the colonies of Britain, France, the United States, and the Netherlands were overrun by Japanese forces at the beginning of the war. This led to local resistance efforts, and when the war was over, many who had resisted Japanese rule advocated for independence. The Philippines, for example, gained its independence from the United States in the aftermath of the war. France, on the other hand, was reluctant to grant independence to Indochina, which, after a bloody war, became North and South Vietnam. The United States, increasingly fearful that the Soviet Union would exert its influence in places like Africa, urged its allies in Europe to grant independence to their colonies. Many nations in Africa became independent through this process. India, on the other hand, is an example of a former colony that asserted its independence on its own, demonstrating the power of nationalist movements in the colonies themselves to effect decolonization. Decolonization also led to more decolonization: as former colonies like India gained their independence, they used their influence to promote independence for other nations. 
https://history.state.gov/milestones/1945-1952/asia-and-africa