During the American Revolution, General George Washington is captured (and eventually executed) by British forces. This is the rebellion's darkest hour. Faced with the loss of the war, and their country, the Continental Congress turns to James Roberts to take command of the American army. James Roberts is in fact James Maria Robert Stuart, the third son of the Old Pretender (James Francis Stuart). It was an open secret that Roberts had been living (incognito) as a farmer in North Carolina since the mid 1760's.
General Roberts eventually leads the Americans to victory, with French assistance, at the Battle of Yorktown. This victory pushes the British to seek peace. The Treaty of The Hague ends the war, officially, in 1783. One provision of the treaty is that James Stuart (having discarded his alias) renounce all claims to the thrones of England, Scotland, and Ireland. This he does on behalf of his entire family. This was done without the permission of his older brothers, Bonnie Prince Charlie (the Young Pretender) and Henry Stuart. James Stuart then returned to his farm, forsaking the political opportunites offered by his new country. He is hailed as "the modern Cincinnatus".
The weak Articles of Confederation became the "constitution" of the new United States of America. It quickly became apparent that this government could not hold the new nation together. An economy in tatters and competing western land claims (leading to armed conflict between some of the states) were just some of the reasons leaders called for a convention to reform/rewrite the Articles. The Articles were eventually scrapped. It was decided that the new form of government would be a constitutional monarchy-provided that James Stuart would accept the crown. Reluctantly, James left his plow and accepted the convention's offer and became King James I, the first king of the United States of America.