In 1857, when the Mormon practice of polygamy came to national awareness, President James Buchanan responded to public outcry by sending an army of 2500 soldiers, called the Utah Expedition, to investigate the LDS Church and install a non-LDS governor to replace Brigham Young. In response, Brigham Young imposed martial law, sending the Utah militia to harass the soldiers, a conflict called the Utah War. Young eventually surrendered to federal control when the new territorial governor, Alfred Cumming, arrived in Salt Lake City on April 12, 1858. Most troops pulled out at the beginning of the American Civil War.