Its king, Penda, saw in the rally of the old religion a chance of winning back his people's freedom and giving it the lead among the tribes about it.

Originally mere settlers along the Upper Trent, the position of the Mercians on the Welsh border invited them to widen their possessions by conquest while the rest of their Anglian neighbours were shut off from any chance of expansion.

Their fights along the frontier too kept their warlike energy at its height.
Penda must have already asserted his superiority over the four other English tribes of Mid-Britain before he could have ventured to attack Wessex and tear from it in 628 the country of the Hwiccas and Magesaetas on the Severn.

Even with this accession of strength however he was still no match for Northumbria.

But the war of the English people with the Britons seems at this moment to have died down for a season, and the Mercian ruler boldly broke through the barrier which had parted the two races till now by allying himself with a Welsh King, Cadwallon, for a joint attack on Eadwine.