It was on this day April 5th in 1081 that Alexios I Komnenos was crowned Byzantine Emperor. He inherited an empire on the brink of collapse. In the Balkans the Normans were carving out yet another kingdom in the Mediterranean to add to Sicily and Southern Italy. In the East the Seljuk Turks occupied Anatolia and were moving into the ancient coastal Greek cities. Other Turkic tribes such as the Danishmends were moving in behind the Seljuks.
With tax revenues severely curtailed and unable to recruit new legions Alexios made an appeal to the West. He sent a message to the Pope in Rome, asking for some western soldiers to help him defend the Byzantine Empire from the Turks.
What happened in response was the Crusades. A river of knights and peasants flowed out of the West, through the Byzantine Empire and into the Holy Land. In the process they established a culture of intolerance and hatred that persists between fundamentalist Christians and Muslims today.
Byzantine politics was characterised by negotiation, diplomacy, political maneuvering, treaties, alliances, compromises and constantly shifting positions. Your blood enemy today could be your ally tommorrow. You never completely burned your bridges if you could help it. It might be better to accept the presence of the Seljuks nearby if it kept the Caliphate far away.
The Franks had no understanding of the delicate interplay of Eastern Roman politics. They were shoot first and ask questions later types of knights. In fact most of the Frankish knights who arrived with the crusades were younger sons. The eldest son, the one trained in administration, remained at home to inherit. The younger sons, trained in war to serve their brothers, found new opportunity opening up in the East. A landless adventurer could hope to carve himself out an estate in the lands of Outremer.
Franks could not distinguish between many of the Eastern sects. They slaughtered Armenian Christians beliving them Muslims. They hated Jews even more than the Arabs. They didn’t even like the Byzantines very much, their Orthodox Christian allies, the people who invited them to the East.
The Western knights had a Manichaean view of religion. If you are one of us you are good and on the side of God. If you are against us you are evil. Facing them were Muslims who saw the world in exactly the same way, only Allah is good and the Christians were evil. The crusades brought these polar opposites together and established norms that persist to this day.
The First Crusade established the Crusader Kingdoms in modern day Syria, Lebanon and Palestine/Israel. It gave Alexios back control of Anatolia, but gave him a new headache in the form of Norman and Frankish adventurers. The Western knights had no interest in returning lands to the Byzantine Empire. They wanted to keep what they conquered.
The Crusader Kingdoms barely lasted 300 years on the mainland. In the process they did provide a buffer between the Arabs and Byzantium. Constantinople limped on until 1453 when it fell to another Turkish Tribe, the Ottomans.