During World War II, thousands of Americans enlisted in the military after the attack on Pearl Harbor. Many famous baseball players like Ted Williams also enlisted, putting their baseball careers on hold. To replace the players who went to war, the All American Girls Professional Baseball League was formed, featuring women players. The league gained popularity but eventually folded after the war ended. The commissioner also sent a "Green Light Letter" allowing baseball to continue as a morale boost on the home front. Some Negro League players got opportunities in the major leagues as replacement players during this time as well.