 The moral decline that the knights underwent over the course of this period is best highlighted by the decision of many knights to serve in foreign navies and become "the mercenary sea-dogs of the 14th to 17th centuries", with the French Navy proving the most popular destination.This decision went against the knights' cardinal reason for existence, in that by serving a European power directly they faced the very real possibility that they would be fighting against another Roman Catholic force, as in the few Franco-Spanish naval skirmishes that occurred in this period.The biggest paradox is the fact that for many years the Kingdom of France remained on amicable terms with the Ottoman Empire, the Knights' greatest and bitterest foe and purported sole purpose for existence.