Warfare was endemic in most medieval western European states, for various good reasons. Their rulers were invariably soldiers themselves, and the notables of their dominions, clergy unashamedly included, retained military men. The states had no stable frontiers and though defence might be focused on border castles, even within the territory there were important fortifications in towns and commanding positions which could become centres of military operations. Nor did rulers confine their military objectives to defence. They might effectively deter enemy attacks not only by threats, but also by unprovoked raids, and might trumpet plausible grounds for annexing neighbouring states. Even when rulers had no serious anxieties about their neighbours, they could engage in warfare in order to keep their barons happy by successful campaigning, or to keep them from fighting on their own account. Barons not led to battle by victorious lords were not disposed to meek subservience; only martial distinction commanded uncritical admiration and earned rulers respect. Although successful wars paid for themselves in booty and conquests, great enterprises needed to be launched on an impressively large scale. This was costly, and only rulers with considerable resources and sound credit could compete. Rulers showed resource in efficiently squeezing more out of their ordinary revenues, and ingenuity in devising new reasons for making their subjects pay taxes. Military affairs played an important part in the calculations of the great men, but elude our deeper understanding.