The California Republican Party was founded in Sacramento on April 18, 1856, when the first mass meeting aggregated in the city. When the American Civil War started, the city was strongly pro-Union, although the opposing side, the Confederate States of America, had active supporters within the city. The city of Sacramento's population was alarmed at the possibility of an invasion by forces that were stationed in Confederate Texas when the Union presence stationed within the city was drawn eastwards for battle. As a result, volunteers organized into military defense forces in case an invasion ever would take place.