The perspective of the Byzantine's
Jerusalem wasn’t really important to the Byzantines. It’s just that to get to Islam the crusaders needed to go through Constantinople and the Byzantines still followed roman tradition but there was separation in the church. Emperor Leo in 730 banned all holy images in the church. Praying to these images was thought as a way of bringing luck. Such as stopping poverty or curing the sick. Jerusalem didn’t need to be controlled.
Honestly the Byzantines had no quarries with any of the people fighting. It’s just that they were in the middle and to get to Islam you have to go through the empire. Sadly the crusaders would go through by force. They saw it as a mission of god but the Byzantine saw an invasion force. So they did what had to be done defend their home. So they were just bystanders really.
There politics though were based off the Romans. In fact they consider themselves Romans. Generals were judge’s high commanders and the emperor was in charge of all religion. The Emperor was the highest military commander, the supreme judge and the only legislator, but also the protector of orthodoxy. Constantinople was the center of trade. Fine silk fabrics were woven here and jewelers, goldsmiths, ivory carvers and other craftsmen produced fine artistic works. Architecture, painting, and glassware also achieved high artistic quality.
The area was also a part of the silk rode connected to china.
The second crusade: When he reached the port of Byzantine Conrad the German king sent a letter to the emperor which was really not far from extreme conceit. He said the one with intelligence must know the problem is within but know when to arise. Yeah but there was still battle middle ages right. Yes soon after the franks also came but they came in huge numbers. But the Byzantines were strategist and had great military intelligence. They were well armed and had horses. Yes the Byzantines offered safe passage but they couldn’t reason with barbarians.
The Byzantines were bystanders in a war they didn’t care about. They didn’t need Jerusalem but if they controlled it they would just have another piece of land in their empire. Yes the Byzantines suffered but they survived.