New Model Army troops defeated a larger Royalist force near St Fagans in South Wales on 8 May 1648. Many Royalists were former Parliamentarian soldiers who had mutinied over pay and political grievances. Their defeat ended the principal field resistance supporting the king in Wales.

The battle illustrated the unstable loyalties produced by arrears, disillusionment and competing political promises. Welsh and English accounts framed the rebels either as betrayed soldiers or dangerous instruments of renewed tyranny.