How do labor unions change the lives of workers in the united states?

They negotiate terms with companies and/or government to achieve better working environment for those who work in the US. (Often goes too far though).

in 1897, pershing became a tactical officer at west point, and that's where he was given the nickname "black jack." pershing's first name is "john," for which "jack" is a nickname, and he was a white man who commanded black troops. hence "black jack".