Final answer:
The British shifted their focus to the southern colonies in 1778 after failing to isolate New England and facing the new challenge of France's entry into the war, targeting regions where they expected more support from Loyalists, enslaved people seeking freedom, and Native American allies.
Step-by-step explanation:
The British tried to shift the focus of the Revolutionary War from New England to the South in 1778 primarily because their initial strategy to isolate New England had failed, with the American victory at the Battle of Saratoga serving as a critical turning point. Another considerable factor was the entrance of France into the war on the side of the Americans, which tipped the scales against the British. The southern colonies, with their higher number of Loyalists, slaves desirous of freedom, and potential aid from Native American allies, seemed a more promising theater of war for the British. They hoped these factors, combined with the capture of key southern cities, would allow them to regain initiative and suppress the rebellion more effectively in these areas.