What nation, tribe, religious sect, or other grouping do you like to imaging embarking on an alt-historical migration that has major effects upon the region they chose to settle? My current favorite would be the Purepecha (called Tarascans by the Aztecs) being split by a civil war shortly after the founding of their Mesoamerica state, with the losing faction settling far to the north along the Gila River in Arizona. I find it interesting to speculate what the effects of the metalworking Purepecha among the pueblo-building cultures of the American southwest would be.