World War I was a vast military conflict fought between the Allies, a group of nations including Britain, France, and the United States, and the Central Powers, which consisted principally of Germany and Austria-Hungary. The war originated in Europe due to a web of alliances and treaties which drew in many nations.
During the war, the Minister for Magic, Archer Evermonde, passed legislation forbidding the Wizarding community from getting involved. However, many witches and wizards defied that law and helped their Muggle countrymen in the war (Pm). One of those who joined the war effort was Theseus Scamander, older brother of Newt Scamander. Theseus was known as a war hero (WFT). Newt himself claimed to have helped out with dragons on the Eastern Front of the war (WFT).