Estimates for the total casualties of World War II vary, but most suggest that some 60 million people died in the war, including about 20 million soldiers and 40 million civilians. The Soviet Union lost around 27 million people during the war, about half of all World War II casualties. The largest number of civilian deaths in a single city was 1.2 million citizens dead during the 872-day Siege of Leningrad. Based on 1860 census figures, 8% of all white American males aged 13 to 50 died in the American Civil War. Of the 60 million European soldiers who were mobilized in World War I, 8 million were killed, 7 million were permanently disabled, and 15 million were seriously injured.

In some cases war has stimulated a country's economy (World War II is often credited with bringing America out of the Great Depression). According to the World Bank the event that conflicts subside in the country, and in the event that there is a transition to democracy the following will result in an increase economic growth by encouraging investment of the country and its people, schooling, economic restructuring, public-good provision, and reducing social unrest. Conflict very rarely has positive effects on an economy according to the world bank "Countries bordering conflict zones are facing tremendous budgetary pressure. The World Bank estimates that the influx of more than 630,000 Syrian refugees have cost Jordan over USD 2.5 billion a year. This amounts to 6 percent of GDP and one-fourth of government's annual revenues". One of the most commonly cited benefits for the economy is higher GDP growth. This has occurred throughout all of the conflict periods, other than in the Afghanistan and Iraq war period. Another benefit commonly mentioned is that WWII established the appropriate conditions for future growth and ended the great depression. In previous cases, such as the wars of Louis XIV, the Franco-Prussian War, and World War I, warfare serves only to damage the economy of the countries involved. For example, Russia's involvement in World War I took such a toll on the Russian economy that it almost collapsed and greatly contributed to the start of the Russian Revolution of 1917.