In 1848, the Treaty of Guadalupe Hidalgo ended the Mexican-American War and dramatically reshaped North American geopolitics by ceding half of Mexico's territory to the United States. In the following decades, as conflicts over slavery in the United States and over the nature of nation, state, and religion in Mexico overwhelmed politics, both republics collapsed into civil war. In Mexico, internal conflict sparked foreign intervention and the establishment of monarchical rule under an Austrian prince, while across the border, eleven Southern states seceded from the union to establish a republic founded on slavery and white supremacy. Erika Pani's Torn Asunder weaves these two tales of crisis, war, and political experimentation into a single story. Pani argues that by consecrating these episodes as epic and exceptionalist chapters in both nations' histories, scholars have overlooked the coincidences and connections between the United States and Mexico. She chronicles the ways in which, between 1848 and 1867, politicians from the two nations tested different formulas, reacted to virulent opposition, sedition, and war, and ultimately attempted to unite deeply divided countries. Torn Asunder highlights the fragile, contentious, and unpredictable nature of politics in the Americas, rooted in the inherent instability of popular sovereignty.