 Complete the following phrase:  In the following years, Northumberland occasionally served with the king in France, but his main occupation was the protection of the border to Scotland. At the same time, a feud with the Neville family was developing, particularly with Richard Neville, Earl of Salisbury. This feud became entangled with the conflict between the Dukes of York and Somerset over control of national government. The conflict culminated in the first battle of the Wars of the Roses, at 