Happy Independence Day
This July 4th I wanted to look at the U.S. born players in the NHL who played at least one game during any season. You can see a rise in U.S. players prior to World War 2. After the war, there was a slow increase in U.S. born players until the expansion era (1967). Although 6 new teams were added to the NHL, it took the expansion of 6 more teams by 1974 to increase the number of U.S. born players substantially. More NHL teams in the States = more NHL fans = more hockey camps = more American hockey players.
(source: Quant Hockey)