Sea power may be compared to a chain of three gigantic links: commerce, merchant marine, and navy. Its strength is no greater than that of the weakest link.
In past history, nations have pushed their way upward to commanding positions in two ways: first, by military power and second, by sea power. Sparta, Macedonia, the Roman Republic, Sweden, France, Russia, and Prussia owed their prominence to the aggressive use of military power. Tyre, Athens, Carthage, the Dutch Republic, and Great Britain have depended principally on sea power. The Roman Empire owed its stability to an almost perfect combination of military and sea power.