The Army's never going overseas again after Vietnam. It's all but a certainty.
This is quite possibly the stupidest thing you've ever posted. Vietnam did not reveal anything about the deployability of large-scale military forces. In fact, it strongly supported that it could be done over a very long period. The only damage Vietnam did was to morale. The only thing it taught was that the US could put people out there that long but not accomplish anything without a clear objective.
Iraq and Afghanistan have, by contrasted, stretched the United States Army to and quite possibly beyond the breaking point. They've revealed extreme problems in personnel and procurement over that length of time that probably can't be fixed with the context of the existing military structure. They've revealed the paucity of the ability to meet expeditionary logistical demands over the long term. And finally, they've simply cost far too much in terms of raw capital. We can't
afford to carry out another campaign like that. That they nearly tore the soul of out the Army again is just icing on an ass-shaped cake.
The age of the long-term combat deployment, barring the outbreak of a truly life-or-death struggle, is over. Iraq and Afghanistan sealed what most people had long suspected: a long war is simply no longer affordable. The United States was and is literally the last nation on Earth who could even attempt one at that scale for that period of time, and it will not get cheaper. Eventually the cost rises too high even for the US.