The U-Boat issue helped get the United States into World War I because it angered American citizens and leaders. The American public was mostly upset about the U-Boat issue because it seemed barbaric to them. They did not like the fact that innocent people aboard ships could be killed when torpedoed and sunk by U-Boats. The most important example of this came when the passenger liner Lusitania was sunk, killing over 1000 people. American leaders were also upset about the U-Boat issue because they felt that it violated international law. They felt that the US, as a neutral country, should enjoy freedom of the seas. They did not like the fact that Germany was violating international law. Both of these facts about German use of U-Boats helped cause the US to enter the war.
There were other factors that also helped get the US into the war. One was the Zimmermann Telegram. In this telegram, Germany asked Mexico to enter the war on Germany’s side. In return for Mexico’s help, Germany promised to let Mexico take back the land the US had taken from it in the Mexican-American War. This infuriated Americans when the telegram was revealed. A second factor was the allegation that Germany was engaging in atrocities against people in the countries it conquered. The most notable of these countries was Belgium. There were many stories of massacres and other outrages against Belgian civilians. These stories helped stir up American anger against Germany. All three of these factors helped push the US into WWI.