Final answer:
The city at the focus of the crusaders' efforts was Jerusalem, which was captured during the First Crusade. The Fourth Crusade, however, never reached Jerusalem because the crusaders were diverted to attack Zadar and later sacked Constantinople.
Step-by-step explanation:
The city that was the focus of the crusaders' efforts was Jerusalem, which was captured during the First Crusade in 1099. They established several Crusader States, with Jerusalem as their capital. However, the Fourth Crusade never reached the Holy Land due to distractions and financial issues.
The crusaders were diverted to attack Zara (Zadar) on behalf of Venetian merchants and later became involved in the sacking of Constantinople, failing to make it to Jerusalem or the larger area typically referred to as the Holy Land.