The Great War: Breakthroughs

Harry Turtledove

Is it the war to end all wars - or war without end?
It is 1917 and the United States are fighting a war on two fronts. In the north from the Pacific to Quebec US forces in the air and on land are locked in battle against Canada and Great Britain. To the south at the heart of a line that stretches from the Gulf of California to the Atlantic General Custer intends to do what none of his predecessors have done - to smash through the Confederate lines in Tennessee.
Into this vast seething cauldron plunges a new generation of weapons - submarines barrels attack planes poison gas and flame throwers - changing the shape of war and the balance of power.

'The wizard of If.' Chicago Sun-Times
'The standard-bearer for alternate history.' USA Today