The four bloody Isonzo battles are detailed as well as Conrad’s failed Straf offensive during May 1915. The Austro-Hungarian Army is devastated by the surprising Brusilov offensive June through September and the absence of effective command leadership. The German ally is forced to become involved in order to prevent total defeat, just as it had in 1914 and 1915. Romania’s disastrous entry into the war and a German-led victorious campaign is described. The rapidly declining home front situation is causing increasing starvation and a stirring among the various ethnic groups.

The Caporetto disaster, together with the Russian collapse, threatened the very existence of the Entente. The Allies reacted with unprecedented speed and resolution, accelerating inter-allied integration.

The entry of the United States doomed the Central Powers in the long run but not during 1917, as the collapse of Russia deprived the Allies of their largest army at a time when the Americans could not yet make good the loss. Unable to afford a repeat of the bloody battles of 1916, the Germans resolved to stand on the defensive in the west while the U-boats (and the Bolsheviks) did their work. Meanwhile, the failure of Nivelle’s spring offensive nearly broke the French army, leaving it paralyzed by mutiny for much of the rest of the year, while British and Imperial troops attacked at Arras and Vimy Ridge in the spring, then at Passchendaele in the summer and autumn, gaining little ground at great cost. A November attack at Cambrai, ultimately indecisive, showed how tanks could be used effectively. On other fronts, Russia’s attempt to use Czech deserters against Austria-Hungary was more successful than Germany’s efforts to use Polish deserters against Russia, but not decisively so. The Allies added Greece to their ranks by overthrowing its pro-German king, but nearly lost Italy after the Central Powers achieved a decisive victory at Caporetto, and lost Romania when Russia sued for peace.