Zimmerman Note
German diplomat wrote a letter to Mexican government asking to attack the US in exchange for lands that Mexico used to own in the US
Russian Revolution
Woodrow Wilson did not agree with Russian alliance with the Allies because Russian was totalitarian
Economic issues
loaned lots of money to Allied Powers; if Central Powers won the US wouldn't be paid back
An eyewitness report would be a primary source.
Thhe answer is your last option "led to decline in racist attitudes towards African American and imigrants"
US foreign policy today is hard to describe as its changing with the election of trump but lets say that we were observing the time a bit before this and more in the present-day era.
We used to stay neutral will all countries we could but we began to see that it was not always best to stay neutral (as in the case of WWI and WWII). The failed attempt after World War I to make a league of nations that operated well just demonstrated the problems we had, and was the reason why WWII happened and adolf hitler was able to come to power.
Today, we use economic and military forces on places that are labeled unstable to try and make these places more stable and set up a democratic government.
This for the most part, has failed miserably such as in Syria and Iraq.
Again, mods, please write me if you have concerns over links but I find students learn best sometimes from visuals. This video describes the problem that happened in Iraq/Syria that led to the failure of US troops trying to make the government more stable.
https://www.youtube.com/watch?v=AQPlREDW-Ro
This second video goes more in-depth about the Syrian crisis and shows how US foreign policies affected it.
https://www.youtube.com/watch?v=RvOnXh3NN9w&t=12s