Geography had determined that if a political entity could get to and then control the land ‘from sea to shining sea’, it would be a great power, the greatest history has known. Once that power was achieved, the Union would become almost impossible to invade. As we saw with Russia, there is ‘strategic depth’ for a defending force to fall back to. The size of Canada, (and to a lesser extent Mexico) is also an asset, as any hostile power attempting to invade by going through these countries would have incredibly long supply lines.
