An exploration of the Spanish colonial reaction to the threat of Napoleonic subversion A Great Fear: Luís de Onís and the Shadow War against Napoleon in Spanish America, 1808–1812 explores why Spanish Americans did not take the opportunity to seize independence in this critical period when Spain was overrun by French armies and, arguably, in its weakest state. In the first years after his appointment as Spanish ambassador to the United States, Luís de Onís claimed the heavy responsibility of defending Spanish America from the wave of French spies, subversives, and soldiers whom he believed Napoleon was sending across the Atlantic to undermine the empire. As a leading representative of Spain’s loyalist government in the Americas, Onís played a central role in identifying, framing, and developing what soon became a coordinated response from the colonial bureaucracy to this perceived threat. This crusade had important short-term consequences for the empire. Since it paralleled the emergence of embryonic independence movements against Spanish rule, colonial officials immediately conflated these dangers and attributed anti-Spanish sentiment to foreign conspiracies. Little direct evidence of Napoleon’s efforts at subversion in Spanish America exists. However, on the basis of prodigious research, Hawkins asserts that the fear of French intervention mattered far more than the reality. Reinforced by detailed warnings from Ambassador Onís, who found the United States to be the staging ground for many of the French emissaries, colonial officials and their subjects became convinced that Napoleon posed a real threat. The official reaction to the threat of French intervention increasingly led Spanish authorities to view their subjects with suspicion, as potential enemies rather than allies in the struggle to preserve the empire. In the long term, this climate of fear eroded the legitimacy of the Spanish Crown among Spanish Americans, a process that contributed to the unraveling of the empire by the 1820s. This study draws on documents and official records from both sides of the Hispanic Atlantic, with extensive research conducted in Spain, Guatemala, Argentina, and the United States. Overall, it is a provocative interpretation of the repercussions of Napoleonic intrigue and espionage in the New World and a stellar examination of late Spanish colonialism in the Americas.