There are plenty of examples of rivals or former enemies working together to fight a common enemy throughout history (ex: Britian, Soviet Union, France and the US fighting against Nazi Germany). I'm currently taking AP US History, and I find it fascinating that the natives would ally with the Europeans against rival tribes. Is there any examples of the inverse happening, where natives allied and fought against the Europeans?
Within West Mexico several rival groups banded together to fight off the Spanish in an event known as the Mixton War or the Mixton Rebellion. Groups the Caxcanes, Coca, Zacatecas, and Tephuanos, Tecuexes, and Tequales. These groups rose up against the Spanish in 1540 and fought fiercely for two years before retreating to the remote and mountainous regions of Zacatecas, Nayarit, and Jalisco, being outright slaughtered, or being reduced to such small numbers they were incorporated into other ethnic groups and no longer survive to this day. Those that retreated continued to wage a guerilla war against the Spanish and their native allies all the way up until 1721-1723 when the Nayarit region was forcefully put down by the colonial government.
Pontiac's War in 1763 united Native Americans of various 'tribes' against the British.
Whether all these groups were rivals is a little murkier. Most of the elements assembled against the British in Pontiac's war were not entire 'tribes', and most of these 'tribes' were fairly recent developments, being formed from remnant and refugee communities of groups displaced by English settlement, groups displaced by Iroquois aggression during the Beaver Wars, and groups decimated by epidemic European diseases. They were not "traditional enemies" of one another, though they had probably experienced mutual raiding and conflict.
Pontiac's War was driiven by the British defeat of the French in North America during the French and Indian War. Most of the groups which supported Pontiac had relied on the French, or at least on being able to play the French and the English off against each other, to retain their own independence. Once the British had taken French North America, the position of these Native Americans seemed (and was) much more precarious. Pontiac fought his war as an ally of the French (and in the hope that the French would return). The peace treaty which gave up French claims to their holdings in North America, however, was signed in the same year that Pontiac began his war. The French did not return. Pontiac's forces were defeated or signed peace treaties.