In researching an area in Switzerland (Grisons), I learned that there was a middle ages political alliance known as the Three Leagues, comprised of the League of God's House, the Grey League and the League of the Ten Jurisdictions. I have previously heard about things like the Catholic League, the Lombard League, the Hanseatic League, etc.
My question is: What exactly is a League? Does it just mean, generally, a political collective? If it has such a broad definition, why has its use to describe alliances/collectives fallen out of favor (if that is accurate to say)? If it has a more narrow definition, what is it?
In the case of the Grisons and some other Leagues of the German-speaking area, the original word in this language is Bund, from binden 'to bind together'. In Latin, to bind is ligare, hence the Italian Lega and similar words in Rumantsch. I do not know if the German word Bund is a calque from the Italian lega or vice versa.
That German Bund is really any kind of alliance or collective. Even marriage is a "Bund for life".
That said, the administrative languages of the Three Leagues were German and Latin, not Rumantsch; and in Latin, the word foedus 'pact' is used. The Lombard League called itself a societas 'company'.
In modern German, everything Bundes-... is 'Federal ...' in English, and the modern Romance languages.
So a "League" is an association or alliance or cooperative, and the various leagues that existed are so different from each other on an organisatoric levels, that it is difficult to find something common to all of them. Even the Three leagues each worked in different ways and came about in different circumstances.
And the way I observe it, "League" often seems to serve as a translation for that German Bund because it's a bit shorter than other words and semantically equivalent.
I hope I could clear up more than I muddied. The Three Leagues are very dear to me, so if can help you otherwise I'd be delighted.