During the American Civil War (1861-1865), the average life expectancy of a soldier was about 26 years. This is based on estimates that approximately 620,000 soldiers died out of a total of about 2.5 million who served. However, it is important to note that this average is skewed by the high number of deaths in battle, which were often concentrated among younger soldiers. Many soldiers also died from disease and other causes, which further reduced the average life expectancy.