Why did the u. s. millitary attempt to hunt down mexican revolutionary pancho villa

The US military sent a task force under General Pershing (Forgot his full name, have to search it up) to hunt down mexican revolutionary pancho villa because Pancho Villa, in an effort to get the US to help him out, crossed the border and murdered 18(?) US citizens before retreating back into Mexico. Pershing was sent with a couple thousand troops to hunt him out, but they failed

hope this helps

Iwould say the answer would be b