After mid-1778, the Northern theater of the war became a stalemate, as the main British force remained in New York City and Washington's force was stationed nearby on the Hudson River. The British turned their attention to the Southern theater of the war, launching an ultimately successful expedition to capture Savannah. Though he desired a battlefield command, Greene continued to serve as the Continental Army's quartermaster general. As Congress was increasingly powerless to furnish funds for supplies, Greene became an advocate of a stronger national government. In June 1780, while Washington's main force continued to guard the Hudson River, Greene led a detachment to block the advance of a British contingent through New Jersey. Despite being vastly outnumbered in the Battle of Springfield, Greene forced the withdrawal of the British force on the field. Shortly after the battle, Greene resigned as quartermaster general in a letter that strongly criticized Congress; although some members of Congress were so outraged by the letter that they sought to relieve Greene of his officer's commission, Washington's intervention ensured that Greene retained a position in the Continental Army. After Benedict Arnold defected to the British, Greene briefly served as the commandant of West Point and presided over the execution of John André, Arnold's contact in the British army.