As Rupert lacked the strength to proceed immediately to relieve York, it was agreed at a council of war in Oxford, the King's wartime capital, that he would first move into Lancashire to restore Royalist fortunes, use the Earl of Derby's influence to gather fresh recruits, and secure the port of Liverpool to allow communications with Royalist forces in Ireland.
Given Rupert's inability to swiftly take action to rescue York, a council of war in Oxford determined that he would initially march into Lancashire to boost Royalist prospects, leverage the Earl of Derby's authority to gather additional soldiers, and capture the port of Liverpool to enable communication with Royalist forces in Ireland.