What If America Had Lost the Revolution?
1) Great Britain and Spain would have engaged each other over territorial control in the Americas after 1776, as Spain controlled the territory west of the Mississippi River at the time - constituting almost 2/3 of North America - after France ceded all their territory a decade earlier to both following the Seven Years War (Treaty of Fontainebleau; Treaty of Paris). It's possible that both countries may even have reached a detente of sorts, as the British were in no hurry to expand beyond the Mississippi and banned colonists from settling the area west of the Appalachians in order to maintain that buffer.
2) There would have been no Mexican Empire, because there would have been no American or French revolutions - itself inspired by the American Revolution - to inspire them to rebel against Spain. I am just not a fan of the inevitability of either. Pull that one small thread of a failed American revolution against a powerful empire, and I see others not being as bold to revolt against their own despite their circumstances. The French revolutionaries especially were deeply influenced by the words and deeds of the American founders, who, I believe, would have been executed regardless for their part in the rebellion against Great Britain.
3) Whichever European power seized majority control of the Americas, if any, eventually would have encroached upon, and probably slaughtered, the indigenous nations like the Comanches.
Certainly, there are other subtle nuances of changes to the timeline that could be added to the discussion. But, in my opinion, these are the main highlights of the "what if" scenario.
©2015 Steve Sagarra