The book explains how the Allies, after a series of swingeing defeats, sank their differences and came together to turn the tide against the German Army in the Summer of 1918. Although it is a detailed history of the fighting by British divisions, it also highlights the growing presence of American forces and their huge contribution to victory, too often understated in earlier works. The book deliberately binds together the genesis, size and equipment of the British and American divisions and seeks to inter-mingle the American and British campaigns of 1918.

By blocking the Third German Offensive on the Chemins des Dames and then arriving in time to turn the Kaiser's army out of the Marne salient, the Allied divisions cleared the way for the decisive counter offensive at Amiens. Exhausted and demoralized, the German Army collapsed and the outcome of The Great War was decided.