In the late 19th and early 20th centuries, Mexico's oil reserves became increasingly monopolized by foreign companies, primarily from the United States and the United Kingdom. By the 1930s, dissatisfaction with foreign control and exploitation grew, especially among Mexican nationalists and laborers. President Lázaro Cárdenas, who took office in 1934, sought to address these grievances by promoting land reforms and labor rights. The culmination of these efforts led to the pivotal moment on March 18, 1938, when Cárdenas announced the expropriation of all oil reserves and facilities owned by foreign entities, effectively nationalizing the industry.The expropriation was not merely an economic measure but a bold assertion of Mexican sovereignty amidst widespread social and political changes. Cárdenas's government faced backlash from foreign oil companies and their home governments, particularly the U.S., which threatened economic sanctions and diplomatic repercussions. Nonetheless, the president remained steadfast in his decision, ensuring that the newly formed state-owned entity, Petróleos Mexicanos (Pemex), would operate under Mexican control, prioritizing the nation's welfare and investment in local communities. This essential move transformed the Mexican oil landscape and set a precedent for nationalism in resource management.In the wake of this nationalization, Mexico entered an era of significant oil production expansion, generating substantial revenues that fueled economic development and social reforms. Although tensions remained with foreign governments and companies, Pemex became a symbol of national pride and played a crucial role in Mexico’s post-revolutionary identity. The nationalization of oil ultimately served to reinforce the notion of resource sovereignty throughout Latin America, inspiring similar movements in other countries dealing with foreign exploitation.