Why the United States was not justified to enter world war 1?

The U.S. was compelled to war. On Aug 4th 1914 President Woodrow Wilson proclaimed U.S. neutrality in the war. Although not nearly as clear as WWII, the U.S. did face a threat of national security. The Lusitania was sunk on May 7th 1915 (128 Americans killed). And early in 1917 Germany declared unrestricted submarine warfare, endangering merchant, civilian and military traffic across the Atlantic. Also the Zimmermann Telegram in 1917 was clearly a threat to our security. Basically Germany told Mexico to enter the war on their side and when finished with the campaign in Europe, Germany would wage war with Mexico against the U.S. with the intent of recapturing land that previously belonged to Mexico. This may have only been a threat, but Americans had already died. Congress as well as the President had a duty to defend against any aggression.
It would not have pleased George Washington, but the times were changing.