During the fall of the Western Roman Empire, the Church stepped in to provide stability and services to the people where the empire once did. Church leaders and popes negotiated with barbarians and provided food and aid. The Church then sent missionaries to convert and educate barbarians, transforming their lifestyle and leading to the formation of powerful Christian kingdoms like the Franks and Germans. While the Church united Europe, a new threat arose in Islam. This led to the Crusades between the 11th-13th centuries as Christians tried unsuccessfully to retake the Holy Land from Muslim rule.