The Crusades definitely had an important impact on today’s geopolitical conflicts. The ongoing war in Syria? That conflict was shaped by things that happened during the Crusades, and even before. The ongoing transfer of wealth from the west to the oil-rich countries of the Middle East? That ties back to the Crusades? ISIS? The Palestinian – Jewish conflict in Israel? All of these have some roots in the Crusades of the Middle Ages.
The Crusades were a response by the rulers of western Europe to a conflict that had been going on for a long time. The Europeans sent a couple of armies from Europe into the Holy Land, to re-capture some of their holy sites, that had been previously held by the Byzantine empire. The Byzantine empire, which was Christian, had been in conflict with the Muslim empires of Persia and later the Turks. But the roots of the conflict go back all the way to the Roman Republic.