... “counterfactual” history has become fashionable lately, with historians speculating on paths not taken, in books with titles beginning “What If?” Ian Kershaw doesn’t go quite that far in “Fateful Choices,” but he does attempt to show how one of the most consequential events of the 20th century — World War II — took shape, and why it might have turned out differently.

A professor at the University of Sheffield in England and the author of an acclaimed two-volume biography of Hitler, Kershaw focuses on 10 important decisions by Axis and Allied policy makers in the early years of the war. His contention is that the “fateful choices made by the leaders of the world’s major powers within a mere 19 months, between May 1940 and December 1941,” largely determined the course of future events — not only the outcome of World War II but also the shape of the postwar world.

These are the turning points he chooses:

1) The decision by the British War Cabinet in late May 1940, led by the new prime minister, Winston Churchill, to fight on after the fall of France and not to pursue, as some suggested, a negotiated settlement with Nazi Germany.

2) Hitler’s decision in July 1940 to attack the Soviet Union the following year, ensnaring Germany in a war it could not win. 3) Tokyo’s decision in September 1940 to join the Tripartite Pact with Italy and Germany and to occupy French Indochina. This led to an American embargo on the export of iron and scrap metal and brought conflict with the United States one step closer. 4) Benito Mussolini’s decision in October 1940 to focus the bulk of his war effort not on North Africa, where the British were vulnerable, but on the invasion of Greece, which turned into a debacle that tied down German troops and eventually led to his own downfall. 5) The decision by Franklin Roosevelt in August 1940 to send 50 old American destroyers to Britain, followed by Congress’s approval of the Lend-Lease deal in March 1941, symbolically committing the United States to the anti-Axis cause by (as Roosevelt put it) all “methods short of war.”....

6) Stalin’s failure in the spring of 1941 to heed numerous intelligence reports warning of an impending German invasion — a mistake that cost the Soviet Union dearly when Germany’s Operation Barbarossa began on June 22. 7) Roosevelt’s initiatives in July-August 1941 to embargo oil shipments to Japan, extend conscription, draw up the Atlantic Charter of war aims with Churchill and provide armed escorts to merchant shipping in the western Atlantic — all steps that drew America into an “undeclared war.” 8) The decision reached by the Japanese cabinet and emperor between September and November of 1941 to embark on the southern strategy of grabbing European colonies in the Pacific, beginning with a pre-emptive strike on the United States Navy. 9) Hitler’s decision, in the days following Pearl Harbor, to declare war on the United States, thus sparing Roosevelt the necessity of persuading his countrymen to fight the Nazis as well as the Japanese. 10) Hitler’s decision in the summer and fall of 1941 to begin the mass extermination of European Jewry, making the Holocaust a major feature of the conflict....