I don't know the largest pre-contact war in the Americas, but in North America the largest pre-contact engagement I know of is the Crow Creek Massacre.
In ~1325 AD a village of ~55 lodges was attacked near modern-day Chamberlain, South Dakota. It's inhabitants, at least 486 individuals, were mutilated and killed. I will spare the gory details, but skeletal remains show extensive evidence of both blunt and sharp force trauma. The bodies were exposed for a period of time before someone, we don't know whom, gathered the remains and interred them in the village's fortification ditch. We don't know why the village was attacked, theories usually cite environmental stress and lack of available farmland, and we don't know why such a violent large-scale engagement was undertaken.
I suppose that depends on how you define largest. If by largest you mean "most combatants," then there are a few wars that might be contenders. When the Aztecs attacked the city-state of Coixtlahuacan, the Tlaxcalans and the people of Huexotzinco supported Coixtlahuacan. The Aztec army alone was composed of 200,000 soldiers and 100,000 porters (Hassig 1988:166). Those numbers may be inflated, but demographically speaking they're plausible.
However, that was a relatively short conflict that just involved large armies. Other potential candidates would be 'endemic' conflicts that dragged on for generations, but with few direct large-scale conflicts. The wars between the Aztecs and the Tlaxcalans and Tarascans could potentially top the list on these. There were a few large scale battles in these wars. For example, the Aztecs' attempted invasion of the Tarascan state in 1476 may have involved as many as 80,000 combatants (Gorenstein 1985), but there was also lots of small scale fighting that occurred between these groups for decades. Even though the individual battles were small in number, when you look at these conflicts throughout history they are rather major.
If you're willing to extend "pre-Christopher Columbus" to "pre-contact with Europeans," then the winner probably goes to the Inca Dynastic Civil War between Huascar and Attahualpa, which engulfed virtually the entire Andes as the various panaqas (royal lineages) turned against each other. At the battle of the Yanamarca Valley alone Attahualpa's army had 140,000 soldiers and Huascar's had 130,000 (D'Altroy 2001).
D'Altroy, Terrence. 2001. The Incas. Blackwell Publishing.
Gorenstein, Shirley. 1985. Acambaro: Frontier Settlement on the Tarascan-Aztec Border. Vanderbilt Publications in Anthropology, issue 32.
Hassig, Ross. 1988 Aztec Warfare: Imperial Expanision and Political Control
this is a great question. i know that native north americans are famed for their oral traditions, but is there any written or otherwise documented evidence of any battles pre-contact?