After the Taft-Díaz summit, Burnham led a team of 500 men in guarding mining properties owned by Hammond, J. P. Morgan, and the Guggenheims in the Mexican state of Sonora. Just as the irrigation and mining projects were nearing completion in 1912, a long series of Mexican revolutions began. The final blow to these efforts came in 1917 when Mexico passed laws prohibiting the sale of land to foreigners. Burnham and Hammond carried their properties until 1930 and then sold them to the Mexican government.