I will NPC a lot of the other warlords, but our characters represent the most powerful and influential ones. Most of the lesser warlords command towns or small cities with a battalion or so's worth of troops; they aren't much threat to others yet. But they aren't dumb either; if a powerful warlord starts throwing his weight around and trying to conquer his weaker neighbours, he may find that he had driven them to band together into a new clique. Said clique may equal or even surpass the warlord in strength, making such blatant power plays risky at best.
I'm hesitant to populate the map itself with new warlords for a few reasons, mainly to keep recruitment a possibility and to limit the sheer number of states I need to NPC, so a lot of the minor states will go unnamed unless they become significant. China is a vast country and communication is slow; a lot of what goes on away from the big cities simply isn't seen by a lot of people. For all intents and purposes, a lot of it is no-man's land. For the moment.

1910, so yeah a few bits don't 100% add up, but I'd rather compromise than go full historic accuracy.