I was going to end snappishly with this. Because it’s so much the truth.
https://ip.rflaird.com/2016/02/03/know-what-i-dont-care/
However. You have asked two good questions. Which I will try to answer.
You won’t necessarily like the answers though. Second one first. The victorious allies after the Armistice had just two choices: destroy Germany completely (good); treat Germany very leniently (unacceptable). Wilson’s presence in the treaty process made it possible to collapse utterly between these two poles and punish Germany a lot without destroying them as a nation. Therefore, the pains and deprivations of the Versailles Treaty simply fueled German resentment and enabled them to rise from ruin to vicious vengeance. Hence Hitler.
Back to Question 1. Why did the U.S. enter the war? Wilson promised, promised, promised we never would. But he was a progressive Democrat. He already wanted world government, you know, socialism for the beleaguered idiot millions. He had this thing called the League of Nations in his addled head. He seized on an excuse — because he knew he could change positions on a dime and fool the Rubes — and go “Over There” and “git’er Done”. Because Germany was going to win by pure attrition. The French were clapped out. The Brits had spit and polish but no intestines left. Only Americans could shut down the Huns.
Which they did. Extraordinarily. Leading to the League of Nations. Until Woodrow Wilson couldn’t actually think any better than Hillary or Bernie, being, you know, of an age. Though still well coiffed and bow-tied as a Princeton boy should be. He thought he had sacrificed 100,000 American troops in six months for the greater good. There were big plans to build a Wilson Memorial next to the Jefferson Memorial and for a fifth face at Mount Rushmore, but then he stroked out and forgot to completely die, which is why his wife supervised the disgracefully disrespectful return of the “doughboys” to the United States of America.
Any of this help?