Well to start with the kind of a lame technically correct answer, the early explorers-slash-conquerors of the New World were Spanish or working for the Spanish, and as such would be excluded from any activities in Africa as a result of series of 15th century papal bulls, agreements and treaties (chiefly Alcáçovas and Tordesillas) between Portuguese and Spanish that divided the newly discovered (and to be discovered) lands between the two and established Africa as only Portuguese to take over and medde in which ever way they want.

The above is basically a cop out so let me rephrase your question a bit: why didn't the Portuguese then try to take over Mali?

Well, in fact the beginning of Age of Exploration is inextricably connected with Northwestern Africa and Portuguese ambitions to conquer the area. Which isn't surprising as it is right across the straits. So it should make sense that actually it is Morocco which was the main goal for conquering, not Mali which was much further inland. If nothing else Morocco is an prerequisite if you want to attack from the northern direction. In any case, Portuguese wanted Morocco.

The conquest of Ceuta in 1415 is often touted as a kickstarting Age of Exploration although I would also single out year 1437 when Portuguese failed to take over Tangier and cooled of further military actions in Morocco for a while, and at the same time picked up the seaward voyages south (difficult discussion of causation relationship between these events I will cheekily avoid)

Now, Moroccan conquests would return on the pressed agenda in few decades again, that time successfully, earning king Afonso V the nickname 'African'. It will continue with waxing and waning enthusiasm for a better part of next hundred years, until in poetically ironic twist of events the defeat at Alcacer Quibir and death of king Sebastian would bring downfall of Avis dynasty and Portuguese merger into Spain.

Yet at the peak of their Morocco adventure Portuguese managed to conquer and hold a series of key towns and fortress down the entire coast. But this string of coastal holdings was exactly as described - coastal. Despite all attempts the Portuguese power was unable to penetrate deeper the distance gunshot from the walls. The Moroccans may not be able to push the Portuguese out but neither could Portuguese hold any land securely. All in all, it paints the picture of Portuguese just not having the ability, tools or capacity to conquer much inland.

To go back now to 1430s and the Portuguese sea expeditions down African coast. What spurred this push is being debated but search for sourced of gold is definetly one of the proposed reasons, although to be honest searching for allies against Morocco is pretty high on that list as well. Now these 'expeditions' were without any exeggaration slave raids in its clearest form. The Portuguese were sailing down the sparesly populated coast of Western Sahara, and upon finding remote and unsuspecting villages, attacking them without warning, with intention to take as many of them possible as slaves back with them. And in it they were successful. The resistance they faced was noble but not a match to the experienced military desperate to make money the only way they knew.

With reaching the Senegal and Gambia rivers the Portuguese now faced a different setting. This was a densely populated, more organized societies than the fishing villages they previously hunted. And these had no problems repulsing the Portuguese raids. Unfortunately for the countless souls that were to be sold to slavery, it didn't stop the enslavement. It is not sure how exactly but very quick after the initial hostilities Portuguese managed to broker peace and find locals willing to trade. And soon Portuguese ships were regulary sailing south to 'Guinea' entering bays and rivers and rivermouths and exchanging horses, copper items, textiles for what was primarely slaves supplemented with ivory, gold dust, and other produce. This model of trade, not conquest, with Africa would become the default for the Portuguese for much of the next hundreds of years with the upgrade of establishing fortified year round presence in certain places like Arguin or most famously Elmina (São Jorge da Mina). These feitorias or forts however were not staging grounds for further military actions but merely strongholds to secure continuous trade, give protection from the hostilities of the locals and bases for preventing European interloppers encroaching on Portuguese interests.

And from some testimonies of people assigned to these forts we can imagine why. Because sure enough, those factories were never a popular position to be assigned to, as our sources don't hide to tell. The climate was horrible for Portuguese sensibilities, malaria and other tropical diseases were rampant, and local population always seemed on the verge of 'causing trouble'. There was definetly no room here for conquest, let alone to push all the way to Mali which was a long way from these coastal locations. If it was even a thought, the reality would soon dispel it.

To sum up, Portuguese had other interests and desires, like Morocco and later India and Brazil. When weighed against all the difficulties Saharan and Equatorial Africa had (enemies, climate, deserts and jungles etc) they were more than content with simply trading for gold on relatively favourable terms than conquering all the way to Mali

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!