Ken,
I'd like to hope that our volunteer forces will give us that year in a future major conflict. However, 2 potentially significant differences from the two wars in your list that may have been life threatening to the US as a nation (the 2 World Wars--Korea and VN were neither direct or indirect threats to the continued existence of the American way of life) make me worry.
1.) Today's technology no longer allows the US to rely on the defenses to its national industrial base provided by the Atlantic and Pacific Oceans. US industrial infrastructure could be immediately at risk for attack in a future major conflict. Rebuilding destroyed factories is quite a bit harder than retooling them I believe.
2.) The US all volunteer force is currently the only thing protecting the nation. In both of those earlier "big" wars, the US had at least one ally who was already fully mobilized to stand as a shield while the US took the necessary time to bring its military up to speed. In the case of WWI, those allies were the folks who provided the final training that enabled US forces to succeed on a modern battlefield, not in some low level skirmishes against poorly trained and equipped irregulars or third rate national armies. Today, we would most likely need our combat veterans to do the fighting and would not have an adequate battle-experienced cadre available to train up the additional forces being mobilized. Our newly raised forces would probably have to learn most of their lessons the hard way, as we did in North Africa (at Kassserine Pass among others), Buna, and Guadalcanal--the difference being that we would not have another country's army to cover us while we recover from our mistakes.
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