One nation in turmoil, another seeking aggrandizement, smaller states jostling for security, mercenary expeditions, and political and racial armed struggles breaking out. In 1835 the northern Mexican state of Texas declared its independence and won it after defeating General Santa Anna’s forces at the Battle of San Jacinto. A few years later, as a larger and looming war with the United States approached, the gulf state of Yucatan did the same by claiming itself a separate republic. For Mexican authorities, the existence of breakaway republics on its periphery represented an existential crisis and an opportunity for U.S. and European interests.For many on both sides, the US-Mexican war officially beginning in 1846 after the Republic of Texas was annexed to the United States was merely a continuation of a conflict that began ten years earlier. Adding to the turmoil, the uprising in Yucatan by indigenous Maya against a criollo minority in 1847 and the contemplated military intervention and annexation of that republic by American leadership towards the end of the war sheds light on a conflict with ethnic, national, and international dimensions.In his second transnational history of the Mexican-American War, historian Benjamin J. Swenson examines the breakaway republics of Texas and Yucatan and demonstrates how the war was not only a manifestation of American expansionism and internal Mexican disunion, but a geostrategic contest involving European states seeking to curtail a nascent imperial power’s dominance in North America.