From BR Bullpen
The Civil War, from 1861-1865, had a major effect on the new game of baseball.
Baseball had been invented in the 1840's, and was growing in the 1850's as an amateur game with some players who were paid under the table. The war in 1861 forced most players to become soldiers, but a number of positive things happened to encourage the growth of baseball. First, with the younger players gone, some teams of older players made barnstorming tours during the war, getting fans used to the idea of travelling teams. Second, in the military itself teams were formed that played when fighting was not imminent. Confederate prisoners were introduced to the game when they saw Union soldiers playing it. Frank Bancroft, who later managed in the major leagues, was said to be a force in organizing ballgames during the war.
A SABR research study found that 30 major league players served in the Civil War. See Civil War Veterans Who Played Major League Baseball Research Report. One can only guess at the number of amateur players who might have come later to the majors had they not died in the war.
 Further Reading
- George B. Kirsch: Baseball in Blue and Gray: The National Pastime during the Civil War, Princeton University Press, Princeton, NJ, 2007.
- William J. Ryczek: Baseball's First Inning: A History of the National Pastime Through the Civil War, McFarland, Jefferson, NC, 2009.