BLUF

The USA sits between two oceans, the Pacific and the Atlantic; and it has land borders with Mexico and Canada, neither of which are ever likely to prove a threat to the USA—it is Geography that keeps the USA safe from invasion.

Summary

This article by Blake Stilwell, writing for Military.com, identifies five reasons why geography is the United States' greatest weapon:
  1. The US grew relatively quickly due to abundant natural resources and a massive river system for shipping and transportation.
  2. Two oceans are excellent insulation, and any invader would have to deal with the US Navy's aircraft carriers and submarines.
  3. An invasion of the US would have to come through Canada or Mexico, which would mean crossing difficult terrain.
  4. The American continent is vast, and having to cross east-west would vigorously test the capabilities of any invading force.
  5. The US' topography is a nightmare and would take enemy forces through many kinds of challenging terrain.

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