When did France join World War I?
French entry into World War I
August 3, 1914
France entered World War I on  August 3, 1914, when Germany declared war. France played only a small part in the diplomatic crisis of July 1914–its top leaders were out of the country from July 15 to July 29, when most of the critical decisions were taken.[1][2] Austria and Germany deliberately acted to prevent  the French and Russian leadership from communicating during the last week in July. But this made little difference as French policy in strong support of Russia had been locked in.  Germany realized that a war with Russia meant a war with France, and so its war plans called for an immediate attack on France – through Belgium – hoping for a quick victory before the slow-moving Russians could become a factor. France was a major military and diplomatic player before and after the July crisis, and every power paid close attention to its role.  Historian Joachim Remak says: