Charlemagne and his successors tried to secure the eastern borders of the Frankish Empire in two ways: First through Christianization and through a system of oaths and tribute obligations. However when it was advantageous, they concluded also pragmatic alliances. In their fights with the Saxons, they became allied with the pagan Obodrites; in the case of the Bohemians/Czechs, they made do with the tribute; from the Moymirids, on the other hand, they extorted oaths of allegiance. They interfered into internal affairs, especially skirmishes between individual clans, mainly as mediators and arbitrators. Direct interventions, because of limited resources and an uncertain outcome, were considered only in exceptional cases.