The great European war, for which preparations were being made during the latter part of the nineteenth century, broke out with tremendous fury early in the twentieth. England, Germany, and the United States stood arrayed against France, Russia, Austria, Turkey, Italy, and a number of minor States. The earth was shaken by the convulsion. Torrents of blood were shed; armaments, the greatest that the world has ever seen, were totally annihilated in the terrible whirlwind of shot and pestilence. For a long time it seemed as if Great Britain must sink, overpowered by the vast hosts that beleaguered her, but she eventually came out of the struggle triumphant. Gigantic naval battles were fought at Dover, Gibraltar, Cairo, Constantinople, in the midst of the Atlantic, and in the Indian Ocean, and at last her enemies had not a ship or a colony left.I need some sort of plausible reason for the USA to go along with this. My best guess here so far is secret treaties and one heck of a deal on post-war conditions - e.g. the USA ends up ruling Canada and gets help from its allies to conquer Central and South America etc.
Then the drama was concluded on land. Germany crushed France and Austria in her iron grasp, and England subdued the rest, but not until some millions of her brave sons had perished on the field of battle.
The result of the war was that England obtained the whole of Turkey, a vast piece of the Russian Empire in Asia, and important ports and strongholds in France, Italy, and Spain; while Germany obtained as her share a good slice from France, Italy, and Russia. Shortly afterwards the United States were reunited to England, and the latter entered into a federal union with all the Teutonic States of Europe.
Any better suggestions?