Causes and Effects of the American Civil War The American Civil War began on April 12, 1861 when General Pierre Beauregard opened fire with 50 cannons on Fort Sumter. This marked the beginning of one of the longest and bloodiest wars in American history. It was also the only war that took place fully on American soil. The entire war lasted four years and claimed over 620,000 American lives with many more injured. Causes- Many people attribute the cause of this war to the abolishment of slavery and although that was one of the major catalysts in starting the war it was not the main cause behind th