There are many justifiable, and economical reasons why our nation entered the first Great War. It was considered the first Great War because it was fought between two great powers, which are the Allies and the Central. On April 2, 1917, the United States entered the tournament of world power. The US should've joined the war to pay back Germany for the attacks against the Americans.
On May 7, 1915 the Lusitania which is also the Titanic's sister was sunk without warning by German U-boats it killed over 1200 innocent people, 120 of those innocent people were American citizens. One year later, the Sussex was sunk by German U-boats and American citizens were outraged at these direct violations of their neutral rights at sea. In an attempt to eliminate the threat of American involvement in Europe, Foreign Minister Alfred Zimmerman attempted to provoke Mexico and Japan into attacking the United States with the promise of German assistance the European front was conquered and Mexico's reward would be the majority of the southern United States after the European front was conquered. .
A message containing Zimmerman's intent was decoded by the British and sent to the President Woodrow Wilson of the United States, further swaying Americans to action. Due primarily to submarine warfare and the Zimmerman telegram, President Wilson asked Congress for permission to go to war, and on April 6, 1917, congress officially declared the war.
The first German unrestricted submarine warfare offensive was halted largely due to American pressure (it was also of course partly halted because Germany realized it did not have enough u-boats to win the war). That the USA forced Germany to do this more or less indicates that when and if the Germans resumed the offensive, the position of the USA was going to be highly negative towards them. .