Why did the British Empire collapse?

This is a big question. First, in answering this question, it is helpful to know when the British empire collapsed (could ask back to student for more effective engagement). Most of Britain's colonies were lost in the 20th century, and between 1945 and the 1990s. Knowing this timing, and knowing that Britain's empire was a truly global one, what big global events in the 20th century could have sparked this collapse (ask back to student)? The two world wars were vital. They weakened the British empire in economic terms and damaged its prestige, spurring on powerful anti-colonial movements, like that led by Gandhi in India.We can also take a longer term view, as many historians have, and argue that in an age of modernisation, education and development, the blatant exploitation of British colonialism would prove impossible to sustain. The administrative undertaking of running an empire as big as Britain had by the 20th century also made it overstretched and weak. In this sense, the two world wars were only catalysts, simply hastening an ongoing decline.