Alexander the Great. He loved to conquer, but he preferred if towns just surrendered without a fight. If they did so, and welcomed him, he would reward the town with building construction, Greek culture and a bunch of soldiers wanting to spend their money in the town.
Alexander was not exactly a warlord. He was a
hegemon or ruler which in Greek means he was almost a king. But he was definitely regarded as a legitimate head of state. The term "warlord" implies illegitimacy. A warlord rules by force alone. This question requires a definition of the term.
I would suggest that a warlord is one who uses (and probably has to use) his army to rule.
Alexander, Augustus, and many of the other mentioned here, did not need to use their armies to collect taxes and control the people. They had civilian institutions to do that. Military force was in the background, but civil government also existed. I would suggest that that is not the case with warlords of Africa and with many warlords throughout history. Ironically, I suggests that warlords are not very capable of waging war except against the people they rule. I they leave their realm, they lose it. Given that definition, it would seem to me that it would be difficult, though not necessarily impossible, for a warlord to govern at least a portion of the population with kindness and generosity.