The first major war in Look to the West that is not present in some form in OTL.
The war was sparked by the aftermath of the Second War of Supremacy. During the later, George II of Great Britain had been killed in battle at Dettingen and succeeded by his second son as William IV. William had crushed a Scottish Jacobite rebellion and reached peace with France. However, this peace involved reverting the colonial theatres of the war to status quo ante bellum - which was good for Britain in India, where the BEIC had lost Madras to the French and their allies, but bad in North America where American militiamen had managed to take the French fortress of Louisbourg after a bloody battle and were now asked to hand it back. One of their commanders at that battle had been the exiled Prince Frederick, the Duke of Cornwall, who now seized his chance. Frederick had been building up political contacts throughout the colonies, was a popular local figure, and was shrewd enough to perceive that the growing strength of the American colonies could return to him his birthright. He declared the Empire of North America, with himself as its first Emperor.
William sailed with a fleet under Admiral Byng to America to confront his brother, but Frederick had him assassinated via American riflemen in a fishing boat, blaming the incident on the French. With major conflict averted, Byng cleaved to Frederick and sailed home with American troops. Enroute they learned that Charles Edward Stuart had launched yet another Jacobite rebellion, this time in Ireland. Frederick landed there, defeated and killed Stuart with his Americans, and then returned to Britain in the Second Glorious Revolution.