In at the Death. Settling Accounts, Book Four

Franklin Roosevelt is the assistant secretary of defense. Thomas Dewey is running for president with a blunt-speaking Missourian named Harry Truman at his side. Britain holds onto its desperate alliance with the USA's worst enemy, while a holocaust unfolds in Texas. In Harry Turtledove's compelling, disturbing, and extraordinarily vivid reshaping of American history, a war of secession has triggered a generation of madness.
The tipping point has come at last. The third war in sixty years, this one yet unnamed: a grinding, horrifying series of hostilities and atrocities between two nations sharing the same continent and both calling themselves Americans. At the dawn of 1944, the United States has beaten back a daredevil blitzkrieg from the Confederate States-and a terrible new genie is out of history's bottle: a bomb that may destroy on a scale never imagined before.
In Europe, the new weapon has shattered a stalemate between Germany, England, and Russia. When the trigger is pulled in America, nothing will be the same again. With visionary brilliance, Harry Turtledove brings to a climactic conclusion his monumental, acclaimed drama of a nation's tragedy and the men and women who play their roles-with valor, fear, and folly-on history's greatest stage.