You might want to edit your post to read "armed forces" rather than army. The United States armed forces include Army, Navy, Coast Guard, Marines, Air Force, Space Force (LOL), and the National Guard. I apologize if I left anyone out.
The National Guard is not monolithic either, as it is per service and per state. I.e. Minnesota Air National Guard, Minnesota Army National Guard, Iowa Air… you get it
To clarify the army has 3 types active, national guard and reserve
The reserve doesn’t have combat mos and are primarily support. Active duty soldiers live on bases when not deployed, and train throughout the week like a regular job. The national guard is still part of the army, they train for the same jobs at the same place and wear the exact same uniform. All three departments wear a name tape that says U.S. army.
They just so happen to be in their respective states service, and can be acted on by the governor as well. National guard also does disaster relief when state side. All three departments can be deployed to a conflict internationally.
There are differences, but it's quite difficult to define. There's not a huge political difference except maybe the Marines are stereotypically known to be more right-leaning.