Two things that often traveled together
Many crusaders sincerely believed they were fighting for God. Many also hoped for lands, titles or plunder, and rulers who authorized crusades had political aims too. These motives were not necessarily opposites. A medieval lord could think of conquest as a reward that God allowed, and the result was that religious language was sometimes attached to campaigns whose practical goals were territorial.
Land in the East
The First Crusade ended with leaders establishing their own principalities. Bohemond kept Antioch, though he had sworn to return former Byzantine territory to Emperor Alexios, and Baldwin of Boulogne took Edessa. Godfrey of Bouillon, who had been chosen as ruler of Jerusalem, reportedly declined the title of king. Some chroniclers presented these outcomes as divine reward; the Byzantines regarded them as broken promises.
The Crusader States were colonial in the sense that a Latin Christian elite ruled a mostly local population of Muslims and Eastern Christians. Settlers did exist, but the ruling class stayed small, which made the states dependent on reinforcements from the West.
The Fourth Crusade
The Fourth Crusade (1202-1204) is the clearest example of a holy war that drifted from its goal. The plan was to attack Egypt. The crusaders contracted with Venice for a fleet, but fewer men arrived than expected, and they could not pay the full price. The Venetian leadership proposed that the army help take Zara, a Christian city on the Adriatic, to settle the debt. The pope had forbidden such an attack, and the crusaders were threatened with excommunication, though the sentence was later eased.
A claimant to the Byzantine throne then offered money and support for the crusade if the army restored him. The Byzantine capital was attacked in 1203, and after political upheaval, taken and sacked in April 1204. Churches were looted and relics carried away. Western leaders set up a Latin Empire, which lasted until the Greeks retook the city in 1261. Pope Innocent III was angry at the diversion, but accepted the result. Historians still discuss whether the outcome was planned, or a series of improvisations driven by debt.
Crusades within Europe
Popes also proclaimed crusades against Christians. The Albigensian Crusade, called in 1209, targeted the Cathars and their protectors in southern France. Northern French nobles took part, and the campaigns lasted for years. They ended with the French crown extending its influence across the south, so religious and political outcomes became closely linked. Popes also used crusade language against political enemies such as the German emperor Frederick II, which critics at the time considered a misuse.
The Baltic and Iberia
In the northeast, the Teutonic Knights and other orders fought pagan peoples such as the Prussians and Livonians. The campaigns were presented as missionary war, and the conquests created a state ruled by the order. The orders also settled German colonists in the region.
In Spain, Christian kingdoms expanded south across several centuries. Popes granted crusading indulgences to those who joined campaigns, and the Reconquista is often described in religious terms, though many alliances crossed religious lines and conquest was also driven by local kings’ ambitions.
Reading the evidence
It is tempting to say the religious language was simply a cover for greed. Most historians doubt that. Crusaders often spent more than they gained, and spiritual rewards mattered to them. Equally, it would be naive to ignore the land and power that followed. The better view is that faith and ambition were interwoven, and that contemporaries themselves argued about where legitimate religious war ended and mere conquest began.