How did crusades affect the world today?

They increased the authority of the king: Sometimes nobles died in battle without leaving an heir in which case the king got their land. Kings passed taxes to pay for the crusades. To pay this tax some nobles had to sell some of their land. Other nobles used the sale of land to offer serfs a chance to buy their freedom. Without as much land, nobles did not need as many serfs. As for the peasants, they were free to leave. They simply never had a reason to do so before. Many young men joined the crusades for adventure. If a peasant died, while serving in the crusades, the king got their land as well. With all this influx of land and money paid to them, the Kings grew to have great power.