Professional era

Professional ice hockey has existed from the early 20th century. By 1902, the Western Pennsylvania Hockey League was the first to openly employ professionals. The league joined with teams in Michigan and Ontario to form the first fully professional International Professional Hockey League (IPHL), in 1904. The IPHL hired numerous players from Canada, and Canadian leagues in response started to openly pay players, who played alongside amateurs. The IPHL, cut off from its biggest source of players, disbanded in 1907. By then, several professional hockey leagues were operating in Canada, with leagues in the Manitoba, Ontario and Quebec provinces of Canada.
In 1910, the National Hockey Association (NHA) was formed in Montreal. The NHA would further refine the rules, dropping the rover position, splitting the game into three 20-minute periods and introducing the system of minor and major penalties. After re-organizing as the National Hockey League (NHL) in 1917, the league expanded into the United States in 1924.
Professional ice hockey leagues developed later in Europe. The game of bandy was still popular and amateur leagues leading to national championships were in place. One of the first was the Swiss National League A, founded in 1916. Today, professional leagues have been introduced in most countries of Europe. The top leagues in Europe include the Kontinental Hockey League, the Czech Extraliga, the Finnish SM-liiga and the Swedish Elitserien.