A history of NHL expansion from the Original Six until the addition of Seattle as the 32nd franchise:
1974: Kansas City Scouts and Washington Capitals join to give league 18 teams.
1978: After Seals’ move to Cleveland, merger of Cleveland Barons and Minnesota North Stars gives league 17 teams.
1991: San Jose Sharks become league’s 22nd team to begin new era of expansion.
1998: Nashville Predators join to give league 27 teams.
1999: Atlanta Thrashers join to give league 28 teams.
2017: Vegas Golden Knights join to give league 31 teams.
2018: Seattle approved as 32nd team to begin play in 2021.
Source: Fox Sports