Who where the military leaders during the period of the lord-vassal system?

The military leaders during the period of the lord-vassel system were "shoguns." The Shogun was so powerful that he was the real power and directed the politics of the empire.

 Pope Urban II; The Cross.

Explanation:

Assuming you are referring to the First Crusade, the above are the answers.

After the death of Prophet Muhammed, Muslim armies swept across the Middle East and captured territory belonging to the Byzantine empire which was Christian. The empire appealed for help and the Pope at the time, Urban II, called on Christian kingdoms to defend the Byzantine empire from the Muslims.

This was the First Crusade and the armies that came together had the symbol of the Cross to symbolize the death of Jesus Christ and Christianity in general.