Note: We saw this piece on Quora and knew we just have to republish it here for the benefit if foreign policy and defence strategy wonks. Enjoy.
America’s military capability is unique from the perspective that today’s military might of the world is completely out of balance. The worlds military might combined still does not equate to America’s military capability. If China, Russia, Iran, the UK, France, Germany, Israel, India, North Korea and every other country came together to invade the USA there are numerous obstacles that would need to be overcome.
Firstly, the rest of the world would need to disable America’s nuclear capacity. America’s nuclear arsenal is based on a triad of land, air, and sea delivery systems designed to provide a counterstrike capability. The submarine-launched ballistic missiles in particular are widely accepted as the most survivable element of the US nuclear deterrent as a portion of it is always at sea. The land-based missiles too are difficult to eliminate, as they are in hardened silos in the middle of the country. Any adversary facing the US would need to either be willing to absorb a nuclear attack or develop a ballistic-missile defence system currently beyond the scope of anything technologically feasible. Thus it is virtually impossible to eliminate America’s nuclear arsenal.
Secondly, if somehow the rest of the world could disable America’s nuclear arsenal it would need to get its forces across the pacific and Atlantic to the US continent. The challenge here is the US is the sole country in the world that has the capability to project force across the globe on a large scale. The combined military air-and sealift capability of the rest of the world would is insufficient to get a foothold on the continental United States. The amphibious assault capability of the world’s militaries, excluding the United States, is just too small. If they managed to go undetected, and acquire some beachheads on the US coast (a virtually impossible feat in light of modern surveillance capability) the rest of the world will still be unable to build up a force of any size before being pushed back into the sea. Any adversary would have to seize and use civilian aircraft and ships not designed for non-permissive environments. These ships would require secure bases in Canada and Mexico, since they lack the capability to deliver forces onto unimproved shores. Thus, any attempted invasion of the US would first look like a caravan of vulnerable civilian ships and aircraft. If these forces managed to avoid US attacks and build up, they could then launch an attack over the mainland.
Thirdly, a land invasion would have to come via a land border, with the terrain of the southern border (Mexico) being most conducive to military operations. This is also where the largest US Army armour base happens to be in Texas, which would hinder such an attack. Going through the Northern Canadian border will require this land force to go West, to avoid the Great Lakes and St Lawrence Seaway – and concentrate forces and target population centres and other important strategic points. The issue then is, are the combined forces of the world enough to defeat the US? The challenge here is whilst the rest of the world would outnumber America’s forces it still has to project this to America’s shores and this will require logistical resources that the rest of the world just doesn’t have.
Fourthly, the primary problem here is geography. Just as the vast Russian steppe swallows armies, so would the oceans that surround the US. No matter the manpower or armament, it must be delivered across the Pacific and Atlantic in order to be brought to bear. This is where US naval and air power would destroy most adversaries, far before they reached the US shore. There are not enough aircraft carriers and amphibious warfare ships in the combined navies of the world to force an entry past the US Navy. There are not enough attack fighters to gain air superiority against the US Air Force.
Read the fifth reason here
Zikist Movement Dot Com’s comment: A sixth reason: Haiti’s defeat of Napoleon’s France led to the doubling in size of the US, throught the Louisiana Purchase, making it an extremely large country to occupy. Kudos to Haiti.