Which in modern times no longer affords any real security.
It remains an advantage for us today but that is decreasing with new technology for certain.
The biggest advantage we maintain might be our own natural resources despite the attempts by the democrats to prevent us from harvesting them as well as our technical and industrial might (China is gaining). Distance from an enemy and self-sufficiency is still important but nobody (me included) can know for certain what the new warfare will look like.
The wild card against China is still Japan. Ironic to say that on this date but they remain a very powerful economy and industrial base and as drone warfare becomes more dominant it is hard to predict the future of war.