Mercia was a small kingdom in the middle of England. Its people were pagans. They were not powerful. They did not have a big army.  In the early 7th century, a new King came to the Throne. He was called Penda. He was a warrior and set up a well organised Mercian army. Penda was fed up with being told what to do by Edwin, the powerful Christian King of Northumbria. He decided to make friends with whoever would help him make Mercia strong. These friendships were called 'alliances'. His best alliance was with the British king, Cadwallon of Gwynedd (North Wales). Together, their armies attacked Northumbria and killed Edwin in battle. Their soldiers burnt the homes and the crops of the people & made them their slaves for 3 years. The Mercians came home with lots of treasure. some people think the Staffordshire Hoard was part of this treasure. Cadwallon was eventually killed in battle by Edwin's nephew, King Oswald, but Penda was safe back in Mercia. Mercia was now strong & important. Penda's armies made it big by taking over 6 neighbouring areas as 'sub-kingdoms'. Lots of people were killed in bloody battles, including King Oswald of Northumbria. The East Anglians were worried about invasion from Mercia. They probably strengthened the huge defensive ditches on the borders of their country, but this didn't stop Penda. They were forced to accept him as their 'over-king'. Penda wanted to crush Northumbria once and for all. He took a big army north, but this was a mistake. Oswald's brother, King Oswy, fought back & Penda was killed. It took his son, Wulfhere, 3 years to make himself the next King of Mercia.