Christian kingdoms refer to various states and territories in Europe and the Middle East that were established during the Middle Ages, primarily influenced by the spread of Christianity. These kingdoms often emerged following the fall of the Roman Empire and were characterized by their governance based on Christian principles and the authority of the Church. Notable examples include the Kingdom of Jerusalem, established during the Crusades, and the Kingdom of England, which played a significant role in European politics. These kingdoms often engaged in conflicts with Muslim states and each other, shaping the religious and political landscape of their time.