The document summarizes the Crusades, a series of wars between Christians and Muslims over control of lands including Jerusalem from the 11th to 14th centuries. The Crusades were launched by calls from popes and rulers to expand Christian territory, with many volunteers joining for pardon of sins or seeking a better life. While the Crusades resulted in some Christian victories as they acquired new lands, they ultimately lost control as the newly taken territories were regained by Muslims in the end.