The Earth is a water planet 75%+ oceans, nearly 7 miles deep in spots. Simply put there are two giant islands in the middle of a planet-wide ocean.  One island is the Africa/Europe/Asia land mass seperated by thousands of miles of ocean from the other island, the North and South American continent.  Between these two land masses the balance of power goes to the EurasiAfrica supercontinent because it is larger and has 80% of the plantes people and resources.  Thus for 98% of history the center of power was on the EurasiAfrica side, but where? The easiest to defend spot is the "heartland/breadbasket" in west central Russia a.k.a. Ukraine, denoted by the yellow triangle.  Powerful civilizations sprung up by the blue circles also, but, where too close to the oceans/shores to hold off invasions.

Of course, the giant continent is actually two: Africa joined to Eurasia by a narrow strip of land, the Sinai Peninsula and Israel denoted by the yellow star to the right.  This connecting point, crossroads, is where 3 major civilaztions leading edges abutted and thus was and has been and is to this day a source of constant conclict.

It is this conclict centered on the yellow star on the right side which proliferated out into 1500 years of Christian vs. Islam intrigue  AND 2 world wars, which so weakened the entire continent so as to open the door for the Americas.  One issue holding back the Americas was having to circum-navigate South America in ordre to reach east coast from west via sea routes.  This problem was solved by the Panama Canal denoted by the yellow star on the left.

Thus the keys to USA security are dominating the Earth's oceans, controlling the Panama Canal and keeping the rest of the world busy and off balance so they cannot unite and create a navy to challenge USA supremacy. We dig deeper in Concept #2 "Homeland Security"