The American Civil War was fought in the United States from 1861-65. After a long standing controversy over slavery and state's rights, war broke out in April 1861, when Confederates attacked Fort Sumter in South Carolina, shortly after Abraham Lincoln was elected. The nationalists of the Union proclaimed loyalty to the U.S. Constitution. They faced secessionists of the Confederate States of America advocating states' rights to perpetual slavery and its expansion in the Americas. Among the 34 states in February 1861, seven Southern slave states individually declared their secession to form the Confederate States of America. In 1860 there were only 16,000 US regulars. By 1865, over two million men had served on the federal side. This vast increase was mostly accomplished by recruiting volunteer companies in a city or county (100 men) and then forming them into state regiments (10 companies). Companies were recruited by locale (city/county) and regiments by state. Mixing men from different states in a company might have happened in the US regulars, but in the vastly more numerous volunteer regiments this simply was not common practice.