At war since 1914, a depleted Europe lay in ruins. Only American intervention in 1917 would turn the tide for the Allies against the Central Powers.At war since 1914, a depleted Europe lay in ruins. Only American intervention in 1917 would turn the tide for the Allies against the Central Powers.At war since 1914, a depleted Europe lay in ruins. Only American intervention in 1917 would turn the tide for the Allies against the Central Powers.