Overlordship was a central feature of Anglo-Saxon politics which began before Æthelberht's time; kings were described as overlords as late as the ninth century. The Anglo-Saxon invasion may have involved military coordination of different groups within the invaders, with a leader who had authority over many different groups; Ælle of Sussex may have been such a leader. Once the new states began to form, conflicts among them began. Tribute from dependents could lead to wealth. A weaker state also might ask or pay for the protection of a stronger neighbour against a warlike third state.