The Second World War was fought on such a large scale that it became total war in many countries - this is where the war effort is prioritized above all else, and the entire population and economy are mobilized to support all military endeavors. Germany and Japan were committing over 70 percent of their national income to the war effort in its final years.

There were also notable fluctuations that coincided with major events for corresponding powers. These included the UK's mobilization of its defenses in 1940, after Germany took most of Western Europe; the spike in Soviet military spending after Operation Barbarossa in June, 1941; and the U.S. entry into the war following the Pearl Harbor attacks in December, 1941.

U.S. military spending/defense budget for 2022 was 876.94 billion US dollars, a 8.77% increase from 2021.

<ul style='margin-top:20px;'>

<li>U.S. military spending/defense budget for 2021 was <strong>806.23 billion US dollars</strong>, a <strong>3.58% increase</strong> from 2020.</li>
<li>U.S. military spending/defense budget for 2020 was <strong>778.40 billion US dollars</strong>, a <strong>6% increase</strong> from 2019.</li>
<li>U.S. military spending/defense budget for 2019 was <strong>734.34 billion US dollars</strong>, a <strong>7.6% increase</strong> from 2018.</li>
</ul>Military expenditures data from SIPRI are derived from the NATO definition, which includes all current and capital expenditures on the armed forces, including peacekeeping forces; defense ministries and other government agencies engaged in defense projects; paramilitary forces, if these are judged to be trained and equipped for military operations; and military space activities. Such expenditures include military and civil personnel, including retirement pensions of military personnel and social services for personnel; operation and maintenance; procurement; military research and development; and military aid (in the military expenditures of the donor country).

Between 1688 and 1968, Britain was arguably involved in more wars than any other nation or empire on the planet. During this 280 year period, the British government's investment into it's military strength increased greatly, and this level of investment allowed Britain to become the most powerful nation in the world for the majority of this period. Inflation rates and fluctuation of the pound Sterling's value make it difficult to compare military spending over extended periods of time, however, if we look at when the largest increases occur over short periods of time, then we can see a correlation between Britain's involvement in major wars and also times of great empirical expansion. Rule Britannia Before the twentieth century, Britain was able to become the world's hegemonic power (or the closest thing to it) because of it's military and naval might. In the past, some historians argued that Britain rose to this status accidentally, however it was their investment in military and naval capabilities that allowed them to colonize other civilizations, protect trade routes, and eliminate competition or threats. For example, Britain lost one of it's largest sources of income when the US gained independence in the late 1700s, therefore the government invested five times more money into it's navy than into the army (in 1785), in order to protect it's other colonies and trade routes, and to expand into other parts of the world. In the nineteenth century, the largest influx of cash into the military came in 1815, the same year that Britain and it's allies finally defeated Napoleon. The end of the Napoleonic Wars marked the beginning of the 'Pax Britannica', (1815-1914) which was a century of relative peace between the major European powers, and further expansion of the British Empire. Twentieth Century There was a large increase in military expenditure at the turn of the twentieth century, as the British Empire pushed further into new territories, particularly in Africa (in what is now known as the 'Scramble for Africa'). However, the largest increases came directly after both World Wars. It is also important to note that new budgets were introduced for the Air Force in the First World War, and then for Central Defense following the Second World War. Unfortunately there is no correlating data for the years during the World Wars, as the country was in a state of national emergency during these times, and parliament's system for budget allocation was different than in traditional years. Following the Second World War, Britain's investment in all military branches has increased exponentially, and today, Britain has the seventh highest military budget in the world.

In 1938, the year before the Second World War, the United States had, by far, the largest economy in the world in terms of gross domestic product (GDP). The five Allied Great Powers that emerged victorious from the war, along with the three Axis Tripartite Pact countries that were ultimately defeated made up the eight largest independent economies in 1938.

When values are converted into 1990 international dollars, the U.S. GDP was over 800 billion dollars in 1938, which was more than double that of the second largest economy, the Soviet Union. Even the combined economies of the UK, its dominions, and colonies had a value of just over 680 billion 1990 dollars, showing that the United States had established itself as the world's leading economy during the interwar period (despite the Great Depression).

Interestingly, the British and Dutch colonies had larger combined GDPs than their respective metropoles, which was a key motivator for the Japanese invasion of these territories in East Asia during the war. Trade with neutral and non-belligerent countries also contributed greatly to the economic development of Allied and Axis powers throughout the war; for example, natural resources from Latin America were essential to the American war effort, while German manufacturing was often dependent on Swedish iron supplies.