What if the American Civil War had been interrupted by a British invasion that persuaded the States to reunite? Harry Harrison's Stars and Stripes Triumphant is book three in the resulting alternate-history sequence.
Much action follows, with America winning through in the initial Stars and Stripes Forever--and then striking back at a British Empire still addicted to conquest, in Stars and Stripes in Peril. Even with Ireland now independent, the Brits remain aggressive in 1865 and use their famous mastery of the seas to stifle US trade, arrogantly confiscating ships and cargoes. President Lincoln can't take this lying down...
Harrison loads the odds enthusiastically. The Empire is complacent, stupid, bloated with too many easy victories. Meanwhile all Americans are staunch and indomitable, and US technological know-how (here about 70 years ahead of its time) develops an unbeatable war machine: destroyers, tanks, armoured columns, Blitzkrieg. As General Sherman puts it:
...If this new kind of army attacks in force it can destroy all who stand before it. The faster the attack, the quicker the end of the conflict. That is why I call it lightning war.
Exciting but one-sided clashes follow, with daring US strategy brilliantly dancing rings around the flabby Empire's larger forces. The politics has a cartoon-like simplicity--the Irish Question, for example, was solved forever when America "liberated" the North from British rule and ordered the country to get united. If only!
Harry Harrison is having lots of fun, and his boyish enthusiasm is infectious. In this alternate 19th century, America is wholly altruistic, concerned only for the greatest good of the greatest number and plans to reform even corrupt, royalist Britain with tough love. It's lightweight, slapdash fun.--David Langford