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Why did colonial empires weaken rapidly after World War II?

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Map of North America in 1763 using color coding to show colonial territories: the 13 American colonies in red along the Atlantic coast, other British territory in orange across much of present-day Canada, Spanish territory in purple covering most of the southern and western regions, Russian territory in green in the northwest, and large areas of unclaimed land in white. Major bodies of water such as the Atlantic Ocean, Pacific Ocean, Gulf of Mexico, and Hudson Bay are labeled. — Western colonialism North America during the colonial period.

After World War II, colonial empires experienced rapid decline due to a combination of shifting global power dynamics, internal resistance, and changing domestic attitudes within Europe. The acceleration of decolonization was driven by three primary factors:

Superpower Opposition: The new global superpowers, the United States and the Soviet Union, both opposed traditional colonialism, preferring to exert influence through indirect economic, military, and ideological means.12
Revolutionary Movements: Mass nationalist movements within the colonies engaged in expensive and often violent struggles for independence, which became increasingly difficult for colonial powers to suppress.12
Domestic Exhaustion: The public in western European nations, weary from the devastation of the war, grew increasingly unwilling to support the significant financial and human sacrifices required to maintain overseas territories.12

Additionally, international pressure mounted through institutions like the United Nations, which actively facilitated the transition to independence for former colonies. By the mid-1970s, these forces had rendered the maintenance of vast colonial empires unsustainable, leading to the emergence of numerous new sovereign states.3415