How far did economics rather than ideology cause WW2?

The short answer

• The Depression and a closing world. World trade’s dollar value fell by roughly two-thirds between 1929 and 1933. Governments also raised barriers: the United States passed Smoot–Hawley in 1930, and Britain adopted imperial preference in 1932. Japan already possessed an empire, yet its leaders saw competitors controlling markets and raw materials elsewhere. If trade was being organized into protected blocs, some reasoned, Japan needed a larger bloc of its own. Manchuria became a ‘lifeline’; Hitler would later call the east ‘living space.’
• The Washington order and its limits. The Washington treaties of the 1920s offered rules for the Pacific: naval ratios, the Open Door in China and consultation among powers. Their force depended on governments respecting them or acting when they were broken. The League had no army, and Britain and the United States were unwilling or unable to commit force to reverse the seizure of Manchuria. China could appeal to agreements, but the agreements did not automatically bring protection.
• The army and the cabinet. Japan’s army claimed a direct relationship with the Emperor rather than ordinary subordination to the prime minister. That left Tokyo with a difficult problem when officers in the field disobeyed. Kwantung Army officers guarding the Manchurian railway concession assassinated the warlord Zhang Zuolin in 1928 and escaped effective punishment. In 1931 the army minister sent a general to check another plot, but word of the visit reached the officers concerned. Civilian weakness would matter when they acted.
• China’s divided position. Chiang Kai-shek’s Nationalists had nominally unified China in 1928, but their government faced rival warlords and communist bases in the south. Catastrophic Yangtze floods added to its troubles in 1931. Japanese radicals expected Nanking to seek legal help abroad rather than offer effective immediate military resistance. They were less attentive to what repeated concessions and humiliation could do over time: resentment could strengthen Chinese nationalism.

What it changed

A pretext takes shape. In the summer of 1931, Kwantung Army staff officers Ishiwara and Itagaki prepared a railway incident, choosing where to place the explosive charge. The next chapter follows their plan into the night of the explosion.

The Weimar center weakens. The European map shows another political consequence of the slump. Weimar’s last majority government fell in 1930, and by late 1932 the Nazis were the largest party in a fragmented Reichstag, though they had no majority. Chapter 3 follows the bargain that brought Hitler to office.

The democracies and defense. Economic pressure also affected the democracies’ defenses. They reduced military spending, while Britain’s ‘ten-year rule’ assumed that a major war was not imminent. As threats grew, those decisions left the democracies less prepared; the advantage to an aggressor varied with the country and theater.