Greatest Hockey Legends has an interesting essay about the effect of war on the game of hockey. Its an engrossing read and I encourage everyone to check it out.
In response to the dilution of talent during World War II, the league changed its rules to encourage a faster paced game. Until 1943, a player was not allowed to make a forward pass across his own blue line. That changed in the 1943-44 season, when the NHL ruled that players could pass from their defensive zone up to the middle of the rink, which would be marked by a new red line at center ice. This changed the game drastically, as many returning war veterans discovered upon their return. Also, regular season overtime had to be discontinued due to wartime curfew restrictions. OT would not return for 41 years.