What is one long term effect of the crusades on the modern world?

This is not an easy question to answer.

It had an immediate and profound effect on Europe especially the 3rd Crusade. Here 2 of the most powerful monarchs decided to fight for a noble cause (freeing Jerusalem). When the cat's away, the mice will play. A great deal of power was exchanged especially in England (and France, but France was not as dramatic as England). English monarchs up until then had almost absolute power including the power of the purse strings. All that changed when John was left on the throne while Richard was off earning the name Lionhearted. The result was English democracy was born. That's one long term effect.