**Question 1:** The event that signaled the end of the Byzantine Empire is **the fall of Constantinople**.
**Question 2:** The event that was MOST DIRECTLY responsible for increased tensions between Byzantine and western Christians during the Crusades is **Crusaders attacked Constantinople on their way to Egypt**. The sack of Constantinople in 1204 during the Fourth Crusade worsened the relationship between the Orthodox and Roman Catholic Churches and weakened the Byzantine Empire.