Unlike predecessor empires, the Venetian imperium did not stand on tribute wrested from subjugated lands. Theirs was built on sea routes; small but well-defended surveillance, water and food supply stations in the Aegean islands; and strong trading relationships. Venetian ships carried spices and silk to English Channel ports and returned with wool and wine. They traded extensively with the Byzantines and sailed into the Black Sea to fill their hulls with westbound grain. They connected northern European products to markets in the Levant and beyond.

But when the world began to change, Venice failed to adapt. Its senate weakly supported the Byzantines as the Ottomans overwhelmed them, capturing Constantinople in 1453 and renaming it Istanbul. Its nobles, wrongly calculating that they could trade with anyone, grasped neither the Islamizing ambitions of the Ottoman sultans nor their own strategic peril as the Turks expanded their navy and swallowed up important Venetian ports.

Instead, Venice turned its face from the Adriatic and joined the internecine wars that consumed the Italian city states during the Renaissance. Nobles who had once looked exclusively to seaborne trade tended new estates in Tuscany and Lombardy. When finding rowers for their galleys became a problem, Venice alienated trading partners by raiding the eastern Adriatic shores for slaves. When they raised tax rates on goods that were transshipped through their ports, they drove the carrying trade elsewhere — most notably to northern European hulls that were better constructed to sail in the newly discovered routes around the Cape of Good Hope to India and beyond.

American parallels

American seapower has not always mirrored these mistakes, but the parallels, even when the courses lead in opposite directions, are striking. We have not written off the effects of an Islamizing Muslim world but rather linked our fortunes deeply to curbing it. Beginning with Desert Shield in 1990, the U.S. has been sporadically involved in land wars in the Middle East for more than two decades. As Venice shifted its gaze landward, our own attention to the Middle East's several conflicts has diverted the public's attention away from seapower and the favorable international order that is a major benefit of being a global and dominant seapower. As Venetian nobles believed that trade could trump everything else, including threats to their security from growing Ottoman seapower, so the conventional idea continues to dominate in the U.S. that the amount of trade and the increasingly related economic relationship between the U.S. and China rules out conflict.

Simultaneously, we have over the past quarter century more than halved the size of our combat fleet while China has expanded its navy from a coastal force to one that now operates an aircraft carrier whose prospective blue-water deployment the Chinese official news agency announced toward the end of April.

In "Mayday: The Decline of American Naval Supremacy," recently out from Overlook Press, I examine the parallel between England's descent from great power status and the decimation of its naval power and look at the same path set earlier by the Dutch. The book traces the tandem rise of American wealth and international status alongside our expanding ability to project seapower and shift it easily between the world's great oceans (once the Panama Canal was built). It shows how through combat, presence, crisis response, humanitarian assistance and eventually nuclear deterrence, American seapower replaced that of the Royal Navy as upholder of an international order based on free trade, untrammeled passage on the high seas, and in general, the liberal political principles that we borrowed from the European Enlightenment and which remain the backbone of the U.S.' political existence.

The "Long War" that began before the attacks of September 2001 will continue to absorb our attention as the Muslim world struggles over modernity. This struggle may recede or it may turn more violent than anything we have yet seen. But we can confidently predict nuclear proliferation, the effort to blunt American power projection by denying us access to large parts of the ocean from which we can influence events by threatening or using force, and the continued rise of Chinese military strength and Russia's growing military reach.

There are many ways we can adapt. We can build smaller, less expensive carriers to add to the existing fleet of supercarriers. We can add to the existing fleet of nuclear submarines by building larger numbers of less expensive attack submarines powered by proven alternatives to nuclear reactors. In each case, this would enlarge and disperse the fleet to the consternation of an enemy and the acknowledgement of our own budget constraints. We can cast aside the political correctness of an equal division of the defense budget in favor of its strategic allocation among the military services. We can radically reform the design, purchase and construction of military equipment, discarding today's massive centrally run bureaucracy in favor of flattened, decentralized and accountable institutions, thus saving billions of dollars. The U.S. is not without options to rebuild its seapower and assure its global dominance long into the future. The question that faces us is whether — like other great states that have gone before, no less in their strength than in their dependence on the seas to assert it — we still possess the will.

We can therefore begin a national debate over the value of seapower, or accept without deliberation a long, slow decline into status as a lesser power.