Wilson, along with the American public, felt that going to war was both necessary and wise for a number of different reasons. The overwhelming reason was that the war was crucial in order to make the world safe for democracy. The U.S. believed that it had a strong devotion to both freedom and democracy, and that the sooner the rest of the world accepted those principals the better. Entering the war would help foster democracy in other nations by blunting the power of more aggressive, imperial nations like Germany and the Ottoman Empire.
Underneath this veneer of moralism was a more practical goal. The U.S. had loaned large amounts of money to the allies, and if they lost those debts might not be repaid. Financial security was also a chief goal for the U.S. upon entering the Great War.
Also, the German military decided to allow unrestricted U-boat warfare as the war continued, and soon the U.S. was losing ships as they crossed the Atlantic. Protecting shipping became another chief goal of the U.S. during World War I.
Another aim was the security of its own borders. Germany had sent a proposition to Mexico that asked the U.S.’s southern neighbor to join forced with Germany in exchange for territorial rights that Mexico had long claimed after the Mexican-American War. Hoping to end future allied proposition, the U.S. entered World War I.
President Wilson dragged a reluctant country into World War I after Germany stepped up its submarine attacks on U.S. vessels in an attempt to cut supply lines from the United States to the Allies for long enough to win the war. The Germans calculated their renewed assault in early 1917 would bring the U.S. into the war, but also reasoned that they would have won the war by the time the U.S. mobilized.
Though the U.S. public was largely wedded to isolationism, and Wilson himself agonized over the decision, he felt the time had come to do something about the European situation. He, of course, wanted to defeat Germany, but he had a larger vision and hoped that by entering the war, the U.S. would have much greater influence on the subsequent peace process. He outlined four goals: larger and smaller nations (by which he meant more powerful and less powerful) being treated equally, the creation of an international association to mediate conflicts (this would become the League of Nations and later the UN), the end of nations trying to grab territory from each other, and the end of the private arms trade, which encouraged companies to support war for profit. In other words, Wilson paradoxically entered the war to try to end wars: this was the "war to end all wars."