A Space Force? Let's look at some history and use it to judge what might become a Space Force.
The first United States Army was the Continental Army, created by the Second Continental Congress in 1775. After the Revolutionary War, it was disbanded except for some 80 soldiers because the American revolutionary leaders considered standing armies a threat to republicanism. They didn't want to be up against some military coupmeister. Congress authorized a First American Regiment at this time, but that was about it. Most of the infant United States's army was state militias. But after the defeat of General Arthur St. Clair's army in Ohio by some Native Americans in 1791, Congress authorized the creation of a standing army, the Legion of the United States, and it was renamed the United States Army in 1795. However, the creators of the US Constitution carefully specified that a civilian was to be the Commander in Chief of all the US's armed forces: the President.
Likewise, the first United States Navy was the Continental Navy, and it was also disbanded after the Revolutionary War. But to stop smuggling, the US Congress established its Revenue Cutter Service in 1790, and to fight the Barbary pirates of North Africa, the US Congress established the US Navy in 1794. The RCS eventually became the main part of the US Coast Guard in 1915.
The first United States Marine Corps was the Continental Marines, complete with being disbanded after the Revolutionary War. It was restarted in 1798.
Turning to the United States Air Force, it originated as the US Army Air Forces in 1907, but it only became independent in 1947.
So the US Army, Navy, Marines, and Coast Guard are almost as old as the US itself, while the US Air Force is much more recent -- and it originated out of the US Army.