It has been a question that makes me wonder, since the very first time I read about the history of the Aztecs. In the fall of Tenochtitlan, as commonly known, the Tlaxcalans (Tlaxcaltecs) was the major force, accompanied with many indigenous factions (including even factions in the Triple Aliance itself!), summed up to many 100,000s. When compared with the Spanish troops, which had only around 500-1000 men, the Spanish force was very very tiny.
Given the above facts, it is somewhat counterintuitive that, after the fall of Tenochtitlan, Spain instead of Tlaxcala seemed to be the primary dominant power in the territory, and Tlaxcalans played a more passive role (even in the process of the conquest the Tlaxcalans seemed to play a subordinate role to the Spanish, not at an equal status, despite being major force).
Why did the conquest end up this way?