Most of the tensions that provoked the First World War were caused by years of struggles for hegemony in the European continent by the Triple Alliance formed by Germany, Austria-Hungary and Italy (though Italy switched sides when it entered the war in 1915) and the Entente formed by Britain, France and Russia. Germany, in particular, seemed the most powerful of American enemies as it competed with Britain for world leadership. Americans feared that an expansion of German influence would lead to increased militarism and reduced democracy. Germany was a powerful military force and, as the war began, its army made important victories. However, as the war dragged on, neither of the two sides were able to force the other to surrender. Germany's naval dominance, an apparent strength, was the immediate cause for American entrance in the conflict. The German announcement of undistinguished submarine warfare led Americans to fear for the safety of their own merchant ships and thus come out of their neutrality. The ethnic tensions within Austria-Hungary and the Ottoman Empire were certainly one of the main weaknesses of American enemies.