 With the promulgation of the Mexican Constitution of 1917, the Mexican government was empowered to expropriate natural resources.The U.S. had considerable business interests in Mexico, especially oil, and the threat of Mexican economic nationalism to big oil companies meant that diplomatic recognition could hinge on Mexican compromise in implementing the constitution.In 1923 when the Mexican presidential elections were on the horizon, Obregón began negotiating with the U.S. government in earnest, with the two governments signing the Bucareli Treaty.