Some European monarchs responded positively to Mongol inquiries, but became vague and evasive when asked to actually commit troops and resources. Logistics also became more complex – the Egyptian Mamluks were genuinely concerned about the threat of another wave of Crusader forces, so each time the Mamluks captured another castle or port, instead of occupying it, they systematically destroyed it so that it could never be used again. This both made it more difficult for the Crusaders to plan military operations, and increased the expense of those operations. Monarchs in Western Europe often gave to the idea of going on crusade, as a way of making an emotional appeal to their subjects, but in reality they would take years to prepare, and sometimes never actually left for Outremer. Internal wars in Europe, such as the War of the Vespers, were also distracting attention, and making it less likely for European nobles to want to commit their military to the Crusades, when they were more needed at home.