The war between germany and the allies formally ended with the

signing of the treaty of versailles

formation of the league of nations

meeting of the congress of vienna

signing of the treaty of brest-litovsk

It's the signing of the Treaty of Versailles

i believe the answer is a

although world war i began in 1914, the united states did not join the war until 1917. the additional firepower, resources, and soldiers of the u.s. to tip the balance of the war in favor of the allies. remaining neutral. when war broke out in 1914, the united states had a policy of neutrality.