What caused industrial psychologists to begin working with the military?

What caused industrial psychologists to begin working with the military was U.S. entry into WWI.
After years of upholding its isolationist policy of not getting involved with any wars it has nothing to do with, the US actually decided to go back on that decision and join the WWI. This is why many psychologists started working with the army in order to help the soldiers.

1. Britain repealed all of the Townshend Act expect the tea tax. 
2. The Boston Tea Party occurred.
3. The Committees of Correspondence and Safety were established.