To understand nations at war, you have to look at how their economies function. With World War II on the horizon, Europe and Asia dug themselves in for a fight - and a look at each other's resources told them what to expect. European economies were so closely connected that some people expected they have to avoid another world war or destroy their finances, but in fact World War I had taught them how to prepare for just such a scenario. Germany, France, and Great Britain all invested in their military before war broke out. When evaluating these economies to see how war would affect them, we look at four main factors: GDP, population, territorial extent, and per capita income. Broadly, this helps us determine how resilient, expansive, self-sufficient, and developed a nation is. All of those factors determine how a nation must conduct its war. For example, the vast territorial holdings of the British Empire meant that they had vast resources to draw upon but needed a long time to mobilize them, which helped Germany determine that they needed to strike fast and win big if they hoped to win the war before Britain's full resources came into play. Japan also estimated that they could win a war in the Pacific if they managed to win before the US had been involved for more than 6 months. These calculations drove the early strategies of the Axis powers, but the participation of the US would later prove to be a crucial factor.

After Germany's early push, the situation looked dire in Europe. The United States had resources to help out, but initially clung to an isolationist policy. Gradually, measures like Cash and Carry and the Lend-Lease Act expanded their involvement. Germany's blitzkrieg had been largely successful. France fell early, and Great Britain appeared on the verge of collapse. Europe needed more resources to sustain their resistance, but the United States was bound by the Neutrality Act which established a policy of isolationism and forbade the US from supporting foreign wars in any way. President Franklin Delano Roosevelt skirted those restrictions. He lobbied Congress to reinstate a provision in the law called Cash and Carry, which would allow other nations to buy US war materiel with cash and transport it themselves into the warzone. He also established an agreement which allowed him to place American military bases on British colonies in exchange for destroyer ships, thus safeguarding the far reaches of the United Kingdom from possible Axis invasions. When it turned out that the English won the Battle of Britain and successfully staved off the attempted Nazi conquest, America decided to support them in a more substantial, long term way. Thus the Lend-Lease Act was signed: the US would loan equipment to their strategic partners (who were not the Allies yet). Though supposedly the equipment had to be returned, it was pretty obvious that war materiel would not come back in the same shape if at all, so this was really the largest donation of war supplies ever. But it wound up benefiting the US in turn, since the increased production galvanized an economy that had been stagnant since the Great Depression. It also kickstarted the involvement of the US Merchant Marine, who were among the earliest US citizens to give their lives in World War II and suffered the highest casualty percentage of any branch of the service. These unarmed ships navigated U-boat infested waters to bri

The armies and technology of World War II required a vast supply of resources. A close look at Germany and Japan shows how the need to secure those resources played a significent role in determining strategy throughout the war. The armies of World War II needed a vast supply and variety of resources. The Allies had many of those resources on their side, but the Axis powers did not. Germany imported many of its resources from countries it would soon be fighting, and needed their war strategy to account for the acquisition of those resources. The Molotov-Ribbentrop Pact signed with the USSR set up a trade agreement to bring them oil from Russia for a while, in addition to establishing temporary non-aggression with the Soviets. When the war began in earnest, Germany targeted Norway with its supply of aluminum and iron as well as its access to the even more resource-rich Sweden. Conquering France also gave them access to rich farmland to feed the troops. But even though they had gained control of the oil fields in Romania, it wasn't enough to power their war machine. Many Nazi generals wanted to target North Africa for this, but Hitler had his sights set on the Soviet Union and wound up squandering much of Germany's reserves in a fruitless effort there. Meanwhile, Japan's entrance into the war had cost them their primary trading partner: the United States. The Japanese army wanted to pursue the Northern Expansion Doctrine (Hokushin-Ron) and push through China into Siberia, wounding the USSR in the process. They attempted this strategy, but the Soviets met them in Mongolia and pushed them back in the Battle of Khalkhin Gol. So they turned to the Southern Expansion Doctrine (Nanshin-Ron) advocated by the navy, and began to sweep up islands in the Pacific. They planned to strip the European colonial powers of their holdings, and they succeeded in capturing 90% of the world's rubber production. But the US responded by synthesizing rubber, and built an industry so large t

A series of missed airstrikes resulting in the death of civilians sparked the no-holds-barred Battle of Britain. Germany launched a Blitz to bomb London into submission, but inadvertantly sparked more resistance and gave British industry a chance to bounce back. On August 25, 1940, a group of German bomber planes got lost on a night-time mission over England. They wound up dropping bombs not on their industrial target, but on the city of London itself. Winston Churchill ordered a retaliatory strike against Germany, but this time it was the RAF who missed their target and hit civilians. Hitler was convinced this was intentional, so he rescinded his prohibition against targeting civilians. The Luftwaffe organized a massive attack against London, intending to break the British people's will to fight. The Blitz backfired in several respects. First, it diverted Germany's attention from strategic targets, which meant they were no longer putting real pressure on the British industrial war efforts. Second, they wound up bringing the British together and strengthening their will to fight on in the names of those who'd been lost to German bombs. Ultimately, the cost in men and material for Germany to wage the Battle of Britain exceeded the cost of damage they inflicted.