Mexico's 1938 oil expropriation
President Lázaro Cárdenas nationalized foreign oil companies holding decade-old concessions granted under earlier governments, including the Porfirio Díaz era, creating the state company Pemex. The move followed a long labor dispute with Anglo-American firms.
The U.S. and Britain protested; Mexico repaid claims over years while keeping control of its oil.
The expropriation established that resource concessions made under one government can be annulled by a later one.
That is the legal risk shadowing the 100-year U.S. deal if Venezuela holds free elections and a new government declares it unconstitutional.
