The Orthodox and Catholic Churches acted together against Muslims in the 11th century in order to regain Jerusalem, which has of a great importance for Christianity, Judaism and Islam. In 11th century, the Pope Urban II encouraged Christians to take part in holy wars. Religious causes were only visible reasons for the crusades there were also different causes such as economic and political reasons. On the other hand, the crusades had some important effects on the West and the East.
The crusades had great effects on the Western countries in that they caused some modifications in the religious, economic and political issues. Early on, the crusades contributed to the increase in the wealth of the church and the power of the papacy; however, in the course of time, the church lost reliability among Christians. Moreover, thanks to the crusades, commerce flourished between the East and the West. Some Western countries such as Venice, Pisa and Genoa acquired great wealth, and people’s affluence increased and it triggered the period of the Renaissance. Furthermore, thanks to the crusades, the political atmosphere of Europe changed positively. In the middle Ages, the Western kings struggled with feudalism but the crusades contributed to undermine feudalism in the West so, central authority gained power again.
Not only the West but also the East was influenced by the crusades. Owing to the crusades, most of the countries in the Anatolia, Syria and Palestine were faced with economic and political difficulties. The crusaders plundered a lot of cities. Moreover, the crusades stopped the advance of the Turks and the fall of Constantinople was postponed for three centuries. In addition, owing to the crusades, Islamic countries lost ground against The Mongol Invasion.
To sum up, the crusades continued from 11th century to 13th century. The crusades did harm both to the West and the East. Christianity and Islam provided incentives for holy war or jihad but religious causes were used only for show.