That piece is not well thought out in my opinion. The "magical shield" that's been protecting people in developed nations is simple - nukes. Countries with nukes don't get invaded. Countries without nukes, do. It doesn't matter if you're a democracy (which Iran was until they dared question our control over their oil, and so naturally had to be have... monarchy... brought to them), or a little dictatorship with an affinity for rocket building. The primary point of conventional weaponry (from the perspective of a nuclear power) is to fuel proxy wars and enable the invasion of non-nuclear nations.
Of course he's right that if there is a WW3, the United States will lose. As will every other single major power. And how many artillery shells you have won't matter a lick in this. The goal in WW3 will not be to destroy the other nation's military, but to destroy the other nation, such that it can never recover to pose a threat to you again. Every single juicy high-density economic zone in every single country will end up getting nuked to oblivion. New York City, Moscow, San Francisco, Berlin, Paris - these places will, in all probability, simply no longer exist.
Striving to win an unwinnable war is not only painfully myopic, but also just seems like a great way for humanity to kill itself off.