Tlaxcala, meaning place of the corn tortilla, sat higher above sea level than the valley of Mexico. The Tlaxcala like their Mexica opponents were a Nahuatl speaking people and like the Mexica their state comprised of allied cities.
At the coming of the Spanish the Tlaxcala were locked in an ongoing struggle with Mexico that could only end in their subjugation or annihilation. Surrounded by Mexica controlled territory and stripped of allies, a trade embargo was already resulting in shortages of cotton and more importantly salt.
A Flower War had already concluded to Tlaxcalan disadvantage and now martial effort was concentrated on a defensive strategy to repel Mexica incursions. Having a smaller population than Mexico the Tlaxcala had less warriors in general and specifically less professional soldiers.
Their strategy relied on being nearer to resupply of armament and food than the invading Mexica. If the Mexica could be held they would get hungry and go home. Unlike the Mexica the rank and file of Tlaxcalan army were mainly archers.
Within the Tlaxcalan territory lived a minority population of extremely warlike Otomi who when the Spanish arrived were despatched to see them off.
The ensuing battles were, despite high Indian losses, very close fought and some think that had the Tlaxcala persisted they would have destroyed Cortez and his followers. That would still have left them,in a weakened state, to face the Mexica . Instead when a chastened Cortez offered peace and alliance against the Mexica they agreed.
It is likely that both sides considered themselves to be the senior partner.