This is a super complicated question. If anything has left lasting effects on any African country, it is the effect of colonialism, the colonization of Africa. In the age of New Imperialism, Every European power sought land in Africa. The UK, France, Spain, Italy, Portugal, Germany, and Belgium all had African colonies. The withdrawal of Europeans from these countries ultimately left the African people divided politically, economically, and ethnically. The most visible effects of anything in Africa related are linked much stronger to colonialism rather than the Atlantic slave trade.

You could ultimately argue that European intervention and the slave trade had made Africans more bellicose. Of course, war (and slavery) on the African continent was not a foreign concept. African slaves were largely traded to Europeans in exchange for goods. African tribal leaders highly sought a lot of European goods, especially firearms. An African tribe could not sell every able bodied man or woman into slavery, such a thing would collapse their entire society. To satisfy the European demand for slaves, a lot of people who were slaves were prisoners of war, or captured from another tribe. This obviously led to many increased conflicts among African tribes and societies. It is a stretch to say that this made them more warlike, but it definitely increased the amounts of conflicts.

The slave trade gave them exposure, familiarity, and experience with Europe and Europeans. By the time the new age of imperialism came by, it wasn't like they were exposed to Europe for the first time ever. During the days of new imperialism, many Africans were still bitter (rightfully so) that their ancestors were sold, killed, and enslaved, that this sparked political parties and movements of resistance. You are more likely to see lasting effects of colonialism rather than slave trade, for isntance, the Rastafarian movement. This was started by people who believed the King Sellasie was divine because he resisted colonization (but not influence) from the Italians. There are Rastafarians to this day, anywhere you go.

The parts of Africa that were impacted by slavery had weak political and economic systems both before and after slavery/colonization. If you think about it, a poorly run, fragmented African societies would obviously have much draw to technological advances that they could acquire if they traded. An African society and civilization that was stronger, more unified, and independent would be somewhat more different. If you think about it, a large labor force leaving your realm en masse for centuries surely takes a HUGE strain on your economy. After colonization, these parts of Africa were still very politically and economically weak. European withdrawal from Africa, they usually left the countries in bad condition, perhaps you can argue in worse condition, than before colonization. Sudden withdrawals left large power vacuums, people and factions, sometimes these people/factions were aligned by ethnicity, religion, and social class, were all completely fractured. Unfortunately, the people who came in these parts have left Africa synonymous with three things: instability and corruption, and war. War happens in Africa between Muslims and Christians. War has happened over ethnicity and social class, for instance, the Rwanda genocide occurred between two ethnic groups that their former occupiers Belgium believed were superior. Instability and corruption ravages the entire continent. Country names and borders shift in Africa more than they probably should. Corruption runs rampant, where as countries that are rich in resources, often take advantage of the people for labor, and the normal people never see the riches that the government does.

I believe that you can't make this argument with out bringing in colonization. The two do not necessarily go hand in hand, but all but two African countries were colonized, the states that were plundered for slaves no doubt were further affected in ways that were built upon the effects of slavery.