Complex sentence: The conquest of Jerusalem became the prime objective of the First Crusade, which was launched in 1095 with Pope Urban II's call to arms; four main crusader armies left Europe in August 1096.
Split into simpler sentences: The conquest of Jerusalem became the prime objective of the First Crusade, which was launched in 1095 with Pope Urban II's call to arms. Four main crusader armies left Europe in August 1096.