[8] When forces supporting Madero succeeded in overthrowing the Diaz in May 1911, Sommerfeld joined the new president's entourage, first as a personal assistant, then as Mexico's chief of the secret service.
[10] The secret service organization Sommerfeld built included Mexican-Americans, Mexican expatriates, other German agents such as Horst von der Goltz and Arnold Krumm-Heller, as well as two of the most notorious soldiers of fortune of the decade, Sam Dreben and Emil Lewis Holmdahl.
[12] In the spring of 1914, Sommerfeld began working closer with successful Constitutionalist Army General, Pancho Villa, commander of the División del Norte.
The task brought Sommerfeld close to General Hugh Lenox Scott and American Secretary of War, Lindley Miller Garrison, both of whom he assisted numerous times when U.S. nationals found themselves in trouble in Mexico.
[15] When World War I broke out in August 1914, Sommerfeld moved to New York ostensibly to represent Pancho Villa's interests but actually worked for German Naval Attache Karl Boy-Ed.
[16] In his function as a specialist on Mexican affairs, Sommerfeld helped the German government sell arms and ammunition they had bought to keep them out of enemy Entente hands.
Villa's huge army of movement, largely using massed cavalry charges, fell before Obregón's superior strategy and tactics of trenches improvised from agricultural irrigation ditches and machine guns.
The Battle of Columbus resulted in civilian casualties and prompted the U.S., to send General John J. Pershing on a Punitive Mission, which was unsuccessful in its attempt to capture Villa.
Sommerfeld, who had proposed to the German government in May 1915 that he could create an incident which would provoke a war between the U.S. and Mexico, became a prime suspect in Villa's attack on Columbus.