After the leaders of the Mexican Revolution -- Pancho Villa, Alvaro Obregon, Venustiano Carranza and Emiliano Zapata -- removed the despised Victoriano Huerta from power, their fragile alliance disintegrated. By early 1915, Carranza and Villa had declared open hostilities on one another, Zapata fought against anyone who invaded his turf in Morelos and Obregon was forced to pick sides. He went with Carranza, who sent him north to take out Villa. The two titans clashed at the town of Celaya in April, 1915 in a battle that would decisively alter the course of the Revolution.

In 1846, the United States and Mexico went to war. The conflict ended in 1848, and Mexico lost, ceding much of California, New Mexico, Arizona and other western states. Four American soldiers, however, may have never left. Mexican archaeologists have tentatively identified four bodies who may be U.S. soldiers who fell at the battle of Monterrey. DNA tests may be performed and a search of records is being performed to determine the identities of the mystery soldiers. The remains will be sent back to the United States if it is determined that they belong to American soldiers.