Can you clarify your question some?

As on its face its a little "odd" as the professional US Army has never gone anywhere after its reorganization from the Legion of the United States very early in the nation's history. Since then it may have been quite small at times, but was always there, augmented of course by state volunteer units, and later the National Guard and draftees.

Do you mean why the post war draw downs in the total force, which were LARGE, were not as large as might have been?