against whom were the Crusades organised?

There were around eight to ten Crusades against Muslims in the Holy Land, and the prime purpose was to gain control of Jerusalem and other holy places. Except the Fourth Crusade, which was again intended to conquer Muslim controlled Jerusalem, but ended up sacking Christian Constantinople the capital of the Byzantine Empire!

Then there was the Albigensian Crusade in the South of France, aimed at eradicating the Cathar heretics. And, in between the Holy Land Crusades, there were minor Crusades against the Prussians, Bosnians, Wends, Nicapolis, Varna, Belgrade - the list just goes on!

I believe it was muslims.

Actually - not that many people know - but there were LOTS of Crusades. We often think of the ones which went off to take the Holy Land away from the Muslims - but actually the Pope organized Crusades hundreds of times when he wanted to keep control in Europe.

For example, - the Spanish Armada was a Crusade - paid for by indulgences and blessed by the Pope. Didn't work out all that well.

So I'd imagine people often believe that the Crusades were all about Muslims and the Holy Land - but mostly they were about keeping other christian nations in servitude to the church.

I'd imagine the wars of the Reformation against Protestant Germany were also Crusades.

Muslims. The excuse being that Jerusalem was the Christian holy land and Muslim presence was defiling it.