Independent Wales was defined in the centuries after the Romans withdrew from Britain in AD 410. The Welsh achieved this despite Irish and Viking raids and colonisation, despite the growing power of the Anglo-Saxon kingdoms, and despite frequent and often bitter dissension between themselves. Pressure from the east increased from the eleventh century onwards, as the Normans carved out marcher lordships and the Plantagenets intensified English royal overlordship, but native Welsh sovereignty remained intact until Llywelyn ap Gruffudd was killed by Edward I's army in 1282; and even then, the dream of independence remained alive, inspiring an ambitious and almost successful revolt under Owain Glyn Dwr in the fifteenth century. The wars of Welsh independence encompassed centuries of raids, expeditions, battles and sieges, but they were more than a series of military encounters: they were a political process.