keep in mind that mexico only existed as of 1821. before that, it was spanish territory. mexico only possessed alta california for 27 years and mostly in name only. there was even a revolt by the governor in monterery. in addition, in the treaty of guadeloupe hidalgo (which ended the mexican american war and ceded the territory), mexico was compensated to the modern equivalent of billions of us dollars in direct payments and the resolution of financial claims against mexico.
United States