In the late 1800's rich southerners hired militias to invade Baja California. The reason was to get some new slave territories free from the newly slave-free U.S.
One large militia organized in Los Angeles. They were well armed and marched south towards Mexico. They only made it as far as San Diego. In-fighting, lose of interest, and massive egos caused the invaders to disband.
SOURCE: Whitewashed Adobe by William Deverell History professor at USC.