Germany, which is at a disadvantage at sea, declared "unrestricted submarine warfare" in February 19 17. The so-called "unrestricted submarine warfare" is a submarine warfare method announced by the German Admiralty in February 19 17, that is, German submarines can sink any merchant ship bound for British waters without prior warning, with the aim of blocking Britain. 19 14 after the first world war, Germany launched a submarine war against the allies, which dealt a heavy blow to British merchant ships and warships. Later, for fear of opposition from neutral countries such as the United States, we had to adopt "limited submarine warfare." However, on February 4, 2007, 1965438+ German Admiralty officially announced the implementation of "unrestricted submarine warfare" to break the economic difficulties caused by the war deadlock. In order to break Germany's submarine warfare, the Allied Forces mobilized 5000 ships and auxiliary ships and 3000 planes, and finally defeated Germany's "unrestricted submarine warfare", which played a positive role in ensuring the victory of the First World War.

Germany's "unrestricted submarine warfare" caused great losses to American merchant ships. After the outbreak of World War II, US President Wilson issued a "neutral" statement on August 4, 2004. At that time, the American people's anti-war sentiment was high, and Wilson won the vote with the slogan of "saving America from war" and was re-elected as president. The American bourgeoisie also hopes to make a fortune in the war through "neutrality". War has brought great disasters to mankind, but it has also brought great benefits to the "neutral" United States. 1914-1916 years, the total industrial output value of the United States increased from 24.2 billion dollars to 62.4 billion dollars. The United States changed from a debtor country to a creditor country. Before the war, the United States had lent its allies $2.3 billion. During the war, Germany carried out unrestricted submarine warfare, which seriously damaged the arms trade between the United States and its allies, and the contradiction between Germany and Germany became increasingly serious. 19 17 years, the two major military groups were exhausted. The United States' participation in the war at this time can not only win easily, but also help to seize world hegemony after the war. So in February 19 17, the United States announced that it would sever diplomatic relations with Germany on the grounds that Germany resumed unrestricted submarines. 19 17 after the March and February revolution in Russia, the United States was afraid that Russia's withdrawal from the war would lead to the failure of the allies, and the loans to the allies were in vain. So on April 6, 19 17, the United States declared war on Germany. In the same year, on February 7, 65438, the United States declared war on the Austro-Hungarian Empire. America's participation in the war greatly enhanced the economic and military strength of the Allies, and further accelerated the failure of the Allies.