Richard Overy's Why the Allies Won frames the Second World War as a contingent event wherein the margins of victory and defeat for either the Axis or Allies were slim until Germany lost the Battle of Kursk. His explanation of "why the allies won" is broken into eight component chapters: four focus on decisive victories on the battlefield and four advance moral, technical, political, or industrial explanations for allied victory.

The foundation of allied victory occurred when American ingenuity in mass production and technical proficiency allowed the U.S. Navy to win the Battle of the Atlantic. Without the secure shipping lines across the Atlantic, Overy argues, it would have been extremely difficult for the Allies to amass enough manpower and resources to carry out Operation Torch in North Africa or the cross-channel invasion into France in 1944. Other decisive points were the Japanese defeat at Midway, the German defeat at Stalingrad, the German defeat at Kursk, the successful invasion of Normandy, and the Allied successes in the bombing campaigns against Germany. On the whole, Overy offers a simple explanation for allied victory: the Allies won the war because they secured meaningful victories on the battlefield when it mattered most.

Overy rejects the arguments that Germany lost the war primarily because Hitler was a megalomaniac and poor strategist. The Soviet revival at Stalingrad was certainly aided by Hitler's stubbornness. However, the Soviet Union won at Stalingrad because its people and soldiers endured heavy sacrifices, reinvigorated the economy and mass production of war material, and developed a strong counter-offensive that enveloped German forces commanded by Paulus in Stalingrad. The Soviet economic miracle is the signature turning point in the Second World War according to Overy; in 1941-1942 the Soviet economy and army was on the brink of total collapse; in 1942-1943 the Soviets produced more airplanes, tanks, and other war implements than the Germans.

Overy's chapters on technology, morale, political unity, and leadership are especially well-done and persuasive. To take one argument, while Germany possessed the most modern army in 1939-1940, it's army faced a severe de-modernization at the war progressed. The Wehrmacht relied more heavily on horses to haul its supplies, and the plethora of makes and models for its motorcycles, lorries, trucks, and tanks confounded mechanics and produced an inefficiency in mass production techniques. Meanwhile, the Allies relied on 1930s technology with incremental improvements and modifications that allowed the United States, especially, and the Soviet Union to a lesser extent, to mass produce its tanks, planes, and heavy guns.

Of all the reasons for Allied victory, Overy seems to privilege at least three above the rest. First, the German military defeats at Stalingrad and Kursk annihilated more German divisions and crippled more of the Luftwaffe than all the military engagements on the Western Front. Essentially, Soviet victories on the Eastern Front made a two-front war for Germany an extremely difficult situation, if not unwinnable, after western forces landed in Normandy. Second, the Allies gained overall air supremacy by 1943-1944, which made German counter-offensives and defensive maneuvers untenable. Third, the allies possessed far more efficient systems for military management and organization that recognized and promoted talent and genius.

This is a solid book that is both sweeping in its narration of World War II and specific in its arguments. Other writers will surely critique and contest Overy's optimistic assessment of Allied strategic bombing—Overy argues that strategic bombing provided intangible benefits in German/Japanese work absenteeism, demoralization, and production slow-downs that ultimately saved more lives than it costed by bringing the war to a close more rapidly—but many of his reasons for why the Allies won have become influential and enduring.