A defense of the US proper would require a small fraction of what the US actually spends on its military. From David Stockman at davidstockmanscontracorner.com:
When the Cold War officially ended in 1991, Washington could have pivoted back to the pre-1914 status quo ante. That is, to a national security policy of America First because there was literally no significant military threat left on the planet.
Post-Soviet Russia was an economic basket case that couldn’t even meet its military payroll and was melting down and selling the Red Army’s tanks and artillery for scrap. China was just emerging from the Great Helmsman’s economic, political and cultural depredations and had embraced Deng Xiaoping proclamation that “to get rich is glorious”.
The implications of the Red Army’s fiscal demise and China’s electing the path of export mercantilism and Red Capitalism were profound.
Russia couldn’t invade the American homeland in a million years and China chose the route of flooding America with shoes, sheets, shirts, toys and electronics. So doing, it made the rule of the communist elites in Beijing dependent upon keeping the custom of 4,000 Wal-Marts in America, not bombing them out of existence.
In a word, god’s original gift to America—the great moats of the Atlantic and Pacific oceans—had again become the essence of its national security.
After 1991, therefore, there was no nation on the planet that had the remotest capability to mount a conventional military assault on the U.S. homeland; or that would not have bankrupted itself attempting to create the requisite air and sea-based power projection capabilities—a resource drain that would be vastly larger than even the $700 billion the US currently spends on its global armada.
Indeed, in the post-cold war world the only thing the US needed was a modest conventional capacity to defend the shorelines and airspace against any possible rogue assault and a reliable nuclear deterrent against any state foolish enough to attempt nuclear blackmail.
Needless to say, those capacities had already been bought and paid for during the cold war. The triad of minutemen ICBMs, Trident SLBMs (submarines launched nuclear missiles) and long-range stealth bombers cost only a few ten billions annually for operations and maintenance and were more than adequate for the task of deterrence.
Likewise, conventional defense of the U.S. shoreline and airspace against rogues would not require a fraction of today’s 1.3 million active uniformed force—to say nothing of the 800,000 additional reserves and national guard forces and the 765,000 DOD civilians on top of that. Rather than funding 2.9 million personnel, the whole job of national security under a homeland-based America First concept could be done with less than 500,000 military and civilian payrollers.
To continue reading: America First—R.I.P.