The First Battle of the Marne began during World War I.
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Registration of US men aged between 21 and 31 began for troops for WWI.
The Treaty of London was signed by Italy, Britain, France, and Russia.
During World War I, as a soldier, Adolf Hitler was injured by a grenade blast.
Britain declares war on Germany.
Unofficial ceasefires sprang up across World War I's Western Front.
