This week's featured article at the Sobel Wiki is on the Trans-Oceanic War, the last major European war of the 18th century.
In our own history, the French Revolutionary Wars and the Napoleonic Wars of 1792 - 1815 were fundamentally different from the conflicts that had preceded them from 1688 to 1763. The wars of 1688, 1701, 1718, 1740, and 1754 involved the establishment, and then the maintenance, of the balance of power in Europe. The wars can all be summed up as attempts by the British, the Dutch, the Prussians, and the Savoyards to prevent the creation of a continent-dominating union of Spain, France, and/or Austria. In our own history, the American Revolutionary War can be seen as a continuation of this tradition, as the French, Spanish, and Dutch combined to prevent British domination of Europe.
The final wars of the 18th century, though, were different. They were fought by Europe's traditional monarchies to extinguish the radical revolutionary republic that had come to power in France, while the French revolutionaries in their turn attempted to spread their own revolution and overturn the other monarchies as they had overturned their own.
In the Sobel Timeline, though, the nascent French Revolution was put down in 1789, and the French monarchy continued. When the Trans-Oceanic War broke out in 1795, it was a traditional balance-of-power conflict in which the French regent, Marie Antoinette, built a coalition with Austria and Spain for the purpose of seizing control of Prussia and Portugal. She was opposed by an alliance of Prussia, Portugal, and Great Britain (and possibly also the Netherlands, Piedmont-Sardinia, and Russia, though Sobel doesn't specifically mention them).
The point of the Trans-Oceanic War, for Sobel's narrative purposes, was to give his newly-established North American nations of Jefferson and the C.N.A. an excuse to invade and conquer Spain's American colonies, specifically Florida and New Spain. This allowed him to set the stage for the creation of the United States of Mexico, and the coming conflict between the U.S.M. and the C.N.A. that alt-Sobel, at least, regarded as the inevitable rematch between the rebels and loyalists of the 1770s.