Little African resistance to colonizers. Most African countries only got independence when the colonizers left on their own.
After fighting for a long time but they became overpowered because
* No one was fighting Europe in Europe, so they had their hand's free
* The Europeans made pacts between themselves on who colonized which region of Africa so they wouldn't fight between themselves
*All the Africans were being colonised at the same time so they couldn't help one another
So when WW2 broke out and Europe finally had a war on their hands, they had to leave the colonial project behind. WW2 was so bad they had recruit help from the colonised countries and probably with the promise of freedom.