Colonial powers in Africa and decolonization?, homework help

Before WWII, European colonial powers expected to rule African territories for a long time. After the end of the War (1945), when they faced popular demands for independence, the colonies free in less than two decades (1960). Most of the African colonies became independent peacefully. But violent conflicts took place in few colonies such as Algeria, Kenya, Rhodesia (Zimbabwe) and Portuguese colonies of Angola, Mozambique and Guinea Bissau.

Why did the colonial powers (Britain and France, in particular) change their pre-War polices and decide to let the colonies free? What was the impact of the armed uprisings in Algeria and Kenya (Mau Maua movement) in the process of decolonization? Why did armed conflict take place in Algeria, Kenya, Rhodesia/Zimbabwe and Portuguese colonies before independence?