First Crusade 1095. Pope declares crusade against Jerusalem
Second Crusade 1145–1149. Muslims attack and take Edessa, crusade declared on Edessa.
Third Crusade 1189–1192. Saladin attacks Jerusalem, pope declares crusade against Jerusalem.
Fourth Crusade 1201–1204. The Fourth Crusade was initiated in 1202 by Pope Innocent III, with the intention of invading the Holy Land through Egypt. The Venetians, under Doge Enrico Dandolo, gained control of this crusade and diverted it first to the Christian city of Zara (Zadar), then to Constantinople, where they attempted to place a Byzantine exile on the throne. After a series of misunderstandings and outbreaks of violence, the crusaders sacked the city in 1204. (I dunno how you could do this, maybe call a crusade against Constantinople? :hmmm: )
Fifth Crusade 1217–1221. Pope calls a crusade against Jerusalem but encourages the crusaders to attack Cario.
Sixth Crusade 1228–1229. Emperor Frederick II had repeatedly vowed a crusade but failed to live up to his words, for which he was excommunicated by the Pope in 1228. (excommunicate HRE) He nonetheless set sail from Brindisi, landed in Palestine, and through diplomacy he achieved unexpected success: Jerusalem, Nazareth, and Bethlehem were delivered to the crusaders for a period of ten years. (call crusade against Jerusalem?)
Seventh Crusade 1248–1254. In 1244 a Khwarezmian force summoned by Egypt stormed Jerusalem. The crusaders were drawn into battle at La Forbie in Gaza. The crusader army and its Bedouin mercenaries were outnumbered by Baibars' force of Khwarezmian tribesmen and were completely defeated within forty-eight hours. (maybe spawn a stack of Khwarezmian/Egyptian troops if Jerusalem is in Catholic hands? I dunno if thats possible though) Louis IX of France organized a crusade against Egypt from 1248 to 1254. It was a failure, and Louis spent much of the crusade living at the court of the crusader kingdom in Acre. (crusade called against Jerusalem?)
Eighth Crusade 1270. Organized by Louis IX in 1270, initially to come to the aid of the remnants of the crusader states in Syria. However, the crusade was diverted to Tunis, (crusade called against Tunis? I dunno how well that would work) where Louis spent only two months before dying. The Eighth Crusade is sometimes counted as the Seventh, if the Fifth and Sixth Crusades are counted as a single crusade. The Ninth Crusade is sometimes also counted as part of the Eighth.
Ninth Crusade 1271–1272. The future Edward I of England undertook another expedition in 1271, (maybe call a crusade against Damascus or Edessa since they are in Syria) after having accompanied Louis on the Eighth Crusade. He accomplished very little in Syria and retired the following year after a truce. With the fall of Antioch (1268), Tripoli (1289), and Acre (1291), the last traces of the Christian rule in Syria disappeared.
Alexandrian Crusade 1365. This was a minor seaborne crusade against Muslim Alexandria led by Peter I of Cyprus.
More on Crusades.
The Cathar Crusade 1209-1229 Maybe cause a city to rebel, spawn "heretics", and cause the pope to declare a crusade on the settlement.
Teutonic knights attack Lithuania 1291-1410. They also fought the Polish in the 14th century and in 1237 aimed to convert Orthodox Russia to Catholicism. They were defeated by Prince Alexander Nevsky of Novgorod in 1242. Maybe give the HRE lots of troops to fight the Polish/Russians/'Lesser factions' Lithuanians or create an emerging faction.
Map of Teutonic holdings.
More on Teutonic Order.
Treatises of 1520 - Martin Luther excommunicated. Maybe this could trigger lots of "heretics" throughout most of Europe.
I don't know if you can use all these, especially the later crusades, but I though I'd post it anyways.