Rome at its height of power only had 35 Legions (about 350 000 men) to defend the entire empire. Like the US it was a strain on her manpower especially when other civilized nations to her eastern edge (Persia, Parthia, Sassanids, etc) started wars. Rome learned to defend her interests by proxy and local auxillary troops (Romans living in area and local natives) and the Legion was brought in as a coup de grace or as a last resort. Given the political division within this nation, a negative MSM, and a large anti war in our elites (celebs, college professors and etc), it is near impossible to fight a long and drawn out war with our troops. I think we need to look at the Afghan model (Northern Alliance troops, backed by US airpower, SOF/CIA teams) and the recent Somalia war (Ethiopia backed by US airpower, intel and SOF/CIA teams) as our new way of confronting our enemies without evoking the ire of the political opposition in this nation who in the end with the MSM will undermind the war even if we are winning the insurgency. NOTE - no one cried foul when the Ethiopian troops allowed the Somalian warlord troops shoot the jihadist prisoners when the towns were retakened. I guarantee those who supported the jihadist rule were rooted out and shot when the warlord troops retook the towns lost.
You are correct, we have no Scipio Africanus or Marius today. The MSM simply will not allow it.