After the World War One it became increasingly difficult for Britain to hold on to the Empire. It became clear that:
The Treaty of Versailles (1919) promoted 'self-determination', or the right to rule yourself. It was difficult for Britain to support this principle for other countries, but deny it to countries in its Empire.
The British Government had promised Home Rule (the ability to hold their own parliament) to Ireland in 1912. When this was delayed by opposition in the North of the island of Ireland and then WWI, a rebellion known as the Easter Rising was sparked against British rule in 1916.
In the years after the Easter Rising nationalists in Ireland (people who wished to have independence) fought the Irish War of Independence against British forces and police in Ireland.
There was a strong independence movement in India:
During the Second World War, British colonies, including Africa and India, made a significant contribution to the war effort. The empire provided over eight million men for military service and provided essential raw materials and goods to Britain. At the end of the war, colonies believed they had earnt a right to independence from the British Empire.
Britain faced economic problems because of the cost of the war, and it was becoming harder to run the Empire. In addition to the mounting cost of running the empire, President Roosevelt tried to encourage Britain to give freedom to its colonies in Africa. However, Britain didn’t want to give up the colonies completely, so instead of granting them full freedom Britain began to introduce democracy to local areas within the colonies.
Eventually, nationalists in the African colonies felt that enough was enough and started protesting and rioting against the British. Jomo Kenyatta in Kenya and Kwame Nkrumah in the Gold Coast (now Ghana) led these protests. With all of their money problems, Britain could simply not afford to deal with this as well. Eventually, independence was granted to these colonies and, between the 1950s and 1980s, Britain lost control of all of its colonies in Africa.
The British Empire was dismantled and replaced by a voluntary organisation of former colonies called the Commonwealth: