Aethelwulf had the responsibility of protecting his kingdom from the invasion by the Danes when the number and frequency of the attacks increased. In 851 Aethelwulf defeated a Danish army at the battle of Oakley (believed to be somewhere south of the Thames), His eldest son Althelstan fought and beat the Danes at sea off the coast of Kent in what is believed to be the first naval battle.
In 855 Aethelwulf travelled to Rome with his son Alfred to see the Pope. Whilst travelling back he spent time with Charles the Bald, King of the Franks and there he married the King's daughter Judith. Back in Wessex Aethelwulf's second son Athelbald learned of his father's marriage and disapproved. In 858 Athelbald made himself King of Wessex. When Aethelwulf returned he decided not to cause conflict and civil war so he let Athelbald rule in the west of the realm while Aethelwulf ruled in the east. When Aethelwulf died in 858 his wife Judith married her stepson Athelbald.