The Lower Rio Grande Valley of Texas. 

August 1915. 

America's "Dirty War." 

With the Plan de San Diego Guerrillas.

And with their Mexican allies, especially Generalissimo Venustiano Carranza's hand picked military and financial liaison for all things "anti - American," General Nafarrate...

This "military assistance"  included Mexican soldiers -- and sometimes even officers -- disguised in civilian garb.

You might say for "deniability!" :)

Snippets of history:
 
'Skirmishing continued along the river; on the night of August 10,  a private of the 12th Cavalry was killed near Mercedes in a clash with Plan de San Diego guerrillas. .."


And as a consequence:


"[T]he entire 26th Infantry was dispatched from Texas City to garrison Brownsville, Harlingen and Kingsville ...


"[US] artillery was sent to Brownsville to overawe General Nafarrate, the guns were pointed directly at his headquarters in Matamoros...

 "In ordering the move Acting Secretary of War Henry Breckenridge telegraphed Above is urgent and admits no delay..."

Original source: The Texas Rangers and the Mexican Revolution: The Bloodiest Decade, 1910 - 1920.

By Charles Harris III & Louis R. Sadler.

Page 269.

Fascinating read! :)