The MLS, NBA, MLB and NHL are considered mostly as USA leagues but they have teams from Canada. Are there other national leagues (any sport) that are mostly from one country but have teams from other nations?
The North American examples certainly aren't unique.
- Monaco has teams in the French systems for various sports, including both football (Ligue 1) and volleyball.
- A number of examples in the UK football systems:
- The Welsh Cardiff City, Swansea City and Wrexham play in the English system.
- The English Berwick Rangers play in the Scottish system.
- The New Saints, who represent both Llansantffraid-ym-Mechain in Wales and the much larger Oswestry in England, play in the Welsh system.
- The Northern Irish Derry City FC play in the Republic of Ireland system.
- Kontinental Hockey League has teams mostly from Russia (19 in the last season) but also from Belarus, China, Finland, Kazakhstan and Latvia (1 from each in the last season).
- Erste Liga (formerly MOL liga) is an ice-hockey liga with teams from Hungary, Romania, Austria. (And in the past there was also one team from Slovakia and one team from Serbia.)
- Since the 2018-19 season, some Hungarian teams play in Tipsport liga - Slovak ice hockey league.
San Marino Calcio plays in Italian football system.
New Zealand has teams in a range of Australian sports leagues: Warriors in the NRL, Breakers in the NBL, Phoenix in the A-League, and various previous conjoint rugby, cricket and netball competitions.
Liechtenstein does not have a Football League on its own. All Liechtenstein clubs participate in Swiss Leagues.
Teams from both Estonia and Latvia play in Baltic Men Volleyball League.