Christendom had relaxed for far too long. The Fifty Years’ War diverted attention to the rivalry of two spoiled children, vying for the title of Empire, while much larger threats swept across Europa.
The Cuman horde pushed further into the Ruslands. Europeans Kings thought it was the result of their need for territorial expansion, when in fact they were not attacking, they were running. From the East, a greater threat emerged. The Mongol Horde, led by the man they call Genghis Khan, quickly ate the declining Cuman horde. As they pushed from the East, the Cumans pushed west, until they could no longer. Eventually, some Kingdoms like Hungary offered to accept the Cumans if they accepted Christ, which they did. Besides that, Divine Knights who battled the Cumans during their expansion west, and potentially saved the Kingdom of Poland, were awarded land above Poland, where they established the Teutonic Order, whose main purpose was the defense against the Eastern horselords. One of the Cuman Princes actually converted to Christianity and broke away from the horde, establishing the Kingdom of Cumania. Eventually, by 1205, the Cumans were pushed out of Europe and the Mongols took over their land. The issue is the Mongols continued onward, led by their great commander.
During the Council of Bologna in 1210, the Pope called for a Fourth Crusade to combat the Mongol threat. The Crusade was spearheaded by the Holy Roman Emperor and Polish King who lead their armies personally. The War lasted until 1216 and ended in failure. The Pope had planned to win back the Russian realms and restore them to Catholicism, but the Mongols proved difficult to beat, even after the Eastern Roman Empire joined in.
The Fourth Crusade proved to be a failure due to the sheer overwhelming force of the Mongol army. However, it has stopped the regular incursions into Europe which they used to conduct. The War left Constantinople’s walls damaged, and the Balkan region fractured.
The Crusader army battled the Mongols in the Ruslands for years, while the Romans attempted to halt their advance in the Caucasus. The Mongols ended up carving through Bulgaria and setting siege to the Roman capital. They could not breach the walls in time, and the Crusader Army arrived to relieve the City. They were victorious against the Mongols and joined the Romans in celebration. For the first time in a long time, it would seem like the Schism could be mended, in order to unite against a common enemy. However, during the festivities, the Crusaders set fire to a part of Constantinople. It is not known whether this was unintentional. Nevertheless, it set off a chain of events that would result in the sacking of Constantinople and the murder of the Emperor by his Varangian Guard. The City was left in ruin, much like Rosewood only half a century prior. This forever soured relations between East and West. The Roman nobility call for a punitive war against the Catholics, but others are hopeful with the rise of the current Empress. There are rumors going around that a marriage between her and the Holy Roman Emperor could bridge the divide.
The Fourth Crusade served only to halt Mongol invasions, weaken the Church’s authority, decimate the Eastern Roman Empire, fracture the Balkan Peninsula and allow for Muslim conquest in Iberia. With the rise of powers like Tunisia, Morocco, Granada, and Mongolia, Christian Europe faces the greatest threat to its existence since the times of the Death.