Reddit reviews Schemers and Dreamers: Filibustering in Mexico, 1848-1921

That's a pretty neat coincidence. You should read a book called Schemers and Dreamers: Filibustering in Mexico, 1848-1921, which discusses in detail various abortive attempts to carve new American-ruled republics out of northern Mexico. Filibustering in general would be worth studying if you want to do a really deep dive. William Walker, who conquered Nicaragua and ruled it for two years, might be especially interesting. There are several modern books out about him, but I haven't read any of them so I can't offer any recommendations.