The causes of the war, the reasons for its outcome, and even the name of the war itself are subjects of lingering contention today. Based on 1860 census figures, 8% of all white males aged 13 to 43 died in the war, including 6% in the North and 18% in the South. About 56,000 soldiers died in prisons during the Civil War. One reason for the high number of battle deaths during the war was the use of Napoleonic tactics, such as charging. With the advent of more accurate rifled barrels, Minié balls and (near the end of the war for the Union army) repeating firearms such as the Spencer repeating rifle, soldiers were mowed down when standing in lines in the open. This led to the adoption of trench warfare, a style of fighting that defined the better part of World War I.