Rule of the territory passed to Mexican hands at the end of the Mexican War of Independence in 1820. It proved difficult to establish a new republic and govern outlying territories with a history of insubordination at the same time, and New Mexico enjoyed a brief semi-autonomous period resembling the salutary neglect of the American colonies. In American history, this period is often referred to as the "Wild West", in reference to relative absence of Mexican authority, which left the region open to incursion from and settlement by American pioneers.