Why was it difficult to maintain the crusade kingdoms?

Firstly, to begin with their numbers were small. They were very dependent on Western Europe for supplies and soldiers. To make matter worse, the crusading knights often abused and committed atrocities against Eastern Orthodox Christians, Jews, and Muslims in the areas through which they passed. The havoc the zealous crusaders brought on the local populations, especially the Jewish communities, made them hated by all groups throughout the region.