league (n.1)

"alliance," mid-15c., ligg, from French ligue "confederacy, league" (15c.), from Italian lega, from legare "to tie, to bind," from Latin ligare "to bind" (from PIE root *leig- "to tie, bind"). Originally among nations, subsequently extended to political associations (1846) and sports associations (1879). League of Nations is attested from 1917 (created 1919).

itinerary unit in medieval England, distance of about three statute miles, late 14c., ultimately from Late Latin leuga (source also of French lieue, Spanish legua, Italian lega), which is said by Roman writers to be from Gaulish. A vague measure (perhaps originally an hour's hike), in England it was a conventional, not a legal measure, and in English it is found more often in poetic than in practical writing.

"to form a league," 1610s, from league (n.1). Related: Leagued; leaguing.