Spain adopted the Constitution of Cádiz in 1812 as a response to the regime of Joseph Bonaparte, which deposed King Ferdinand VII and inspired dissent throughout Spain. Fondly known as La Pepa, the new Spanish constitution would prove short lived—but long influence the course of history and political theory. Indeed, the Constitution of Cádiz was the first truly liberal European document of the kind—drawing on Rousseau, Locke, and Voltaire, it enumerated universal male suffrage, a constitutional monarchy and democratic parliamentary body, and certain social rights previously restricted in largely closed European states. Though the Constitution of Cádiz would crumble by 1814, the immediate influence of this document was felt by New Spain, which would draft its own document and declare the Mexican Federation in 1824. This paper explores the causal link between these two events, applying theory from Rawls, Polanyi, Mill, and The Federalist Papers to determine how each document differs, where parallels emerge, why each failed to last, and how the lessons from Spain and colonial dissent encouraged Mexico to federate. By offering a textual comparison of each document and weaving in anecdotes from history, this paper provides a robust assessment of two quintessential documents for modern political theory and liberal thought in both Europe and Latin America.