Spanish Flu, WWI and WWII—Key Dates and Facts About the Major 20th Century Events

At a White House press briefing on Monday, President Donald Trump wrongly stated the Spanish flu pandemic of 1918 ended World War II, which started in 1939.

Answering a reporter who asked whether he would have called for his predecessor President Barack Obama to resign if 160,000 people had died of COVID-19 in the U.S., Trump said no.

"Nobody's ever seen anything like this," he said. "The closest thing is, in 1917, they say, right? The great pandemic certainly was a terrible thing where they lost anywhere from 50 to 100 million people. Probably ended the second World War, all the soldiers were sick."

According to the U.S. Centers for Disease Control and Prevention, the outbreak of the Spanish flu was the most severe pandemic in recent history. Caused by the H1N1 virus, it spread around the world between 1918 to 1919, infecting an estimated 500 million people. The virus is thought to have caused 50 million deaths. Of those, around 675,000 were in the U.S.

World War I started in 1914, after Archduke Franz Ferdinand of Austria was assassinated, and ended in 1918, after Germany surrendered and signed an armistice agreement.

After the terms of peace were negotiated, what is known as the Treaty of Versailles was signed on June 28, 1919, between Germany and the Allied Nations. What critics described as the harsh terms of the treaty are argued to be among the causes of WWII and the rise of Adolf Hitler. Germany was required to accept blame for starting WWI, was not allowed to join the League of Nations, had land removed, and was not allowed to have an army of more than 100,000, or any submarines or air force.

The pandemic started in January 1918, and unfolded alongside the war for nine months. According to John Mathews, honorary professorial fellow at the University of Melbourne, writing in The Conversation, "the war played a major role in its spread and severity." WWI saw large numbers of people travel long distances for the first time, enabling the spread of the infectious disease. It persisted after the war as people headed home.

World War II started just over two decades later, after Hitler invaded Poland, prompting France and Britain to declare war. The conflict ended in stages. After Allied troops closed in on Germany from both sides, Hitler killed himself in his Berlin bunker on 30 April.

A surrender document was signed on 8 May. The chain of events triggered by the U.S. detonating atomic bombs on the Japanese cities of Hiroshima and Nagasaki that August, lead to the end of the war.

Correction 08/11 7.55 a.m. ET: This article previously stated the Spanish flu killed an estimated 500 million people. The Spanish flu killed an estimated 50 million people, in 500 million cases.