Final answer:
Britain's third plan to win the American Revolution, known as the southern strategy, involved fighting in the South with the support of Loyalists and enslaved people seeking freedom. Despite initial successes, this strategy ultimately failed due to persistent resistance and assistance for the Continental Army from French forces.
Step-by-step explanation:
Britain's third plan to win the American Revolution called for fighting in the South and relying upon Loyalist support is known as the southern strategy. Lord George Germain and other British leaders believed that they could gain the upper hand with the help of Loyalists, enslaved people seeking freedom, and Native American allies. This strategy initially had great success, demonstrated by the capture of Savannah, the capital of Georgia, in December 1778. However, despite these early victories, the southern strategy ultimately failed. Resistance from the Continental Army, led by figures such as George Washington and Nathanael Greene, as well as crucial French support, led to the British defeat at Yorktown, effectively ending the war.