How did the US involvement in WW1 help to benefit people in the world (other than US citizens)? What positive effect did US involvement in WW1 have...

While America did benefit from being in WWI, other nations did as well.  America sent aid in the form of food to Belgium and Northern France toward the end of the war and in the immediate aftermath.  Herbert Hoover, a man who would be unjustly blamed for the Great Depression, organized this food drive and was considered a supply genius at the time.  He kept millions of people from starving to death.  

America was also important in promoting the idea that people should govern themselves.  Wilson's Fourteen Points helped to create Yugoslavia and the Baltic republics of Estonia, Latvia, and Lithuania.  This helped to at least curtail the ethnic violence that helped to create the conditions that led to WWI.  

Finally, one cannot discount the role of the League of Nations, though it was short-lived and America never joined.  The whole idea that the world's major powers could join an organization and arbitrate issues was momentous.  Before this, nations went to war first, and used arbitration to help end the war--the Russo-Japanese War that took place between 1904 and 1905 is a prime example of this.  Wilson sought a world without war; if nations acted openly without secret alliances, then perhaps they would act fairly and civilly.  While the League of Nations ultimately folded due to a lack of power, one cannot imagine the United Nations forming without its predecessor.  This is perhaps the greatest legacy of America's involvement in WWI.