Answers are :
To pursue after Pancho villa and to protect United States interests
The intervention came in response to the chaos generated in the border with Mexico. It was seen as a risk to American interests and relations with a fragile neighboring government that was weak at the time. The positive side of the dictatorship that was being fought in Mexican territory was a stable government with strong relationships to foreign powers. Any armed conflict generates instability in bilateral relations.
This justified the foreign intervention to Mexican soil where the troops came to want Villa either dead or alive. Mexico was in the midst of a civil war. Pancho Villa was a "caudillo", a local military leader that is also portrayed as a bandit, who attacked Columbine, and raid other villages close to the US border, the most famous is this surprise attack were American citizens in New Mexico. took heavy damage.
