We've talked about their politics and their ancestors, but humanity itself has not really been described in detail -- and it deserves to be. The humans of Azeroth derive from the ancient servitors of the Titans, and their origins lie in the frozen continent of Northrend (indeed, before it was a continent of its own), but they've developed over time into a brash, persevering people of their own who rose to master the Eastern Kingdoms and who had endured two hideous wars with alien invaders, the plague of undeath that shattered their strongest kingdom, and times of chaos and uncertainty. It is humanity that holds the Alliance together today, serving to unite disparate peoples in a collective that grows more cohesive in the face of growing Horde expansionism.
The ultimate drive to exist that has kept humanity going past world-shaking calamities must be respected. When war and strife come, humans have risen to the challenge. Although one of the shortest-lived of Azeroth's native races and possessed of one of the youngest cultures, human have risen on the strength of their determination.