Neutrality

Under the Hague Conventions of 1907 belligerents were forbidden to enter neutral territory or move troops and convoys across it, and a neutral state had to intern soldiers who took refuge on its soil. Neutrality could be permanent, like Belgium's, guaranteed since 1839, or declared for a particular war, as Italy and the United States did in 1914.

The German invasion of Belgium on 4 August 1914 brought Britain into the war and became a symbol of contempt for international law. Many states abandoned neutrality during the war: Italy in 1915, Romania in 1916, the United States and Greece in 1917. The Netherlands, Switzerland, Spain and the Scandinavian countries, among others, stayed neutral to the end, though they felt the effects of the blockade and submarine warfare.