"Pope Urban II (1088-1099) was responsible for assisting Emperor Alexus I (1081-1118) of Constantinople in launching the first crusade. He made one of the most influential speeches in the Middle Ages, calling on Christian princes in Europe to go on a crusade to rescue the Holy Land from the Turks. In the speech given at the Council of Clermont in France, on November 27, 1095, he combined the ideas of making a pilgrimage to the Holy Land with that of waging a holy war against infidels."
dragged this from another thread.
I can think of 2 off the top of my head that were related almost directly to the pope. But mostly the crusades were done IN THE NAME OF religion by a emperor or king. Not that said religion was gonna step in and say "hey...ummm...mind not involving us?"