Complex sentence: In 1095, Pope Urban II had responded to pleas from the flagging Byzantine Empire, summoned the European aristocracy to recapture the Holy Land for Christianity, and in 1099 the knights of the First Crusade captured Jerusalem.
Split into simpler sentences: In 1095, Pope Urban II responded to pleas from the flagging Byzantine Empire and summoned the European aristocracy to recapture the Holy Land for Christianity. In 1099 the knights of the First Crusade captured Jerusalem.