Offa was the son of Thingfrith, a descendant of Eowa of Mercia. Eowa was a king of Mercia who ruled along with his more famous brother Penda of Mercia. In 757 the king of Mercia,Athelbald, was murdered. There was a short civil war between others claiming the throne. An ealdorman named Beornred seized the throne of Mercia but Offa drove him out of Mercia and became king himself that same year. The alliances Athelbald had formed fell apart when Offa came to power. Offa had very little power outside of Mercia for the first several years of his reign.