What factors contribute to the buildup of the crusades?

By modern standards, medieval Europe was a terrifyingly violent place. Physical force was used to achieve all sorts of ends. Lords used violence to exert their influence over their subjects and to pursue feuds with each other for political and financial gain. Issues of international politics were frequently resolved on the battlefield. When they occurred, wars affected everyone in a region through pillage and slaughter. Banditry was rife.