Great War is an alternate history trilogy by Harry Turtledove, which follows How Few Remain. Smarting from two defeats at the hands of a Confederate States of America allied with Great Britain and France, the United States has turned to an alliance with the strengthening German Empire. The US military has been reformed along German lines, and the Republican Party of Abraham Lincoln has collapsed, discredited by the defeats, leaving the Democratic Party and the Socialist Party of America as the main political parties in the United States.

When the Great War breaks out in Europe, both the USA and CSA join almost immediately on the side of their respective allies, and the USA is fighting a two-front war against Canada to the north, and the CSA to the south. In eastern America, the conflict soon bogs down into trench warfare, while in the West the battle lines are more fluid.

The Great War trilogy is followed by the American Empire trilogy. It is preceded by his novel How Few Remain.