How did the Atlantic slave trade get its start?

Answer 1

they got they start from European because Europeans began to enslave African who could be obtained from trading post along the African post

Slavery in Africa predated European contact by thousands of years and was part and parcel of trade, commerce and wealth in African nations. The first European contact leading to the purchase of slaves was from with the Portuguese. Europeans did not go to Africa to "enslave" Africans but rather they went to Africa to purchase slaves already enslaved by African rulers. Excess population was seen as a source of wealth and a commodity of trade by African rulers.

The concept of Europeans stalking Africans to make the slaves is factually inaccurate, a distortion of the reality of the African slave trade and has led to a distorted view of the African slave trade reinforcing racial bias for political purposes.