What is a " residual U.S. force "over the horizon" ?

the 100 year thing McCain is talking about is a Residual Force, troops based out of Iraq like they are in Japan, Guam, Germany , Korea and other places we beat in war to help the new free governtment control peace and have troops established in an area where they can be deployed to the front in that region. The bases have created their own structure by suppling jobs and stuff to the locals . Fort Riley Kansas was a residual force in the 1800s to help bring peace to the settlers on the Cali, Santa Fe and Oregon trails