This is my first D-Day anniversary without the hero of my life, my father, who on the morning of June 6, 1944, was on his belly in the surf at Omaha Beach while ranged automatic weapons tore up sand and flesh around him. Against odds, First Lieutenant Calvin R. Batchelor survived and went forward to win what became the first critical victory in the birth of the American empire.

Sixty-two years later, as our ships of the line patrol the China Sea and our legions garrison the ummah, reloading for the next contest, it is heartening to weigh three lessons of empire (recast from Niall Ferguson’s “Colossus”) that we have learned from examination and experience since we cracked Hitler’s Atlantic Wall.

The primary imperial lesson is that New World prosperity defeats Old World despotism. The front line of American power is the shop window of democracy. Efficient markets in the hands of an enfranchised citizenry are a formula worthy of alchemy. We have enhanced earlier experiments in globalization by the Romans in the Mediterranean and the British in the Atlantic by adding the simplicity of container traffic. What defeated Stalinism and Maoism and their drab factotums was America’s gross domestic product and the speed with which the American dollar invaded the dens of bandits. Liberated Eastern Europe, once the backwater of the Soviet sinkhole, is the hottest pool of liberty on the planet. The capitalist dynamos of Japan, South Korea, Taiwan, and Singapore, constructions of our imperial banking, are the best explanations as to how rapidly we are transforming the Asian oligarchies into credible marketplaces.

However, it is candid to admit, while standing on a plateau of the American bull run, that the economic way ahead is threatened by predictable downturns. The competition for energy and the frailty of the major oil states point to a stormy deflationary cycle such as the British empire endured under Gladstone and Disraeli. Falling prices encourage rising hotheads and the xenophobia of the neighborhood bully.

Victorian Britain just barely outlasted Marxism and the anarchists; now America has lost its footing in the fog of border mania and protectionist dither. The American Empire can ride out the fright and shrug off the drawbridge keepers, but we will be politically and economically drained while taking on rogue and failed states.

This secular threat points to the second imperial lesson: that liberal, aggressive, cosmopolitan empires depend upon the security provided by an indomitable fleet and an invincible army. The Roman senate and the British parliament, could usually recover from mistakes by projecting sea power over distances, and we have added the shock of air power and the artificial intelligence of cyberspace. It is also candid to admit, as we measure the burden of the war on terror, that the American empire has exhausted native manpower as did the Roman and British empires in their times; and yet the demands of the global watchtowers are frantic. Beggarly regions invite warlords with piratical ambitions and hallucinatory visions such as the Goths for Rome, the Mahdists for Britain, and the jihadists for us. Like our predecessors, we must find the confidence to draft liberated clans such as Japan and Poland and the new-born Iraq.

America needs to mobilize its version of Rome’s provincial legions or Britain’s Indian Army, to grow the NATO model to the Eastern Hemisphere, and to prepare to finance allied expeditionary forces and a grand fleet.

The final imperial lesson was present that birthday of the empire when America’s boys crawled into the gunfire of the German Seventh Army on Normandy. It is blunt; and it is meant as sobering to the overwhelmed and weary. Just as there was no way back on D-Day without drowning in the flood tide of the Atlantic, there is now no way back from the rushing 21st century. The noise of the anti-Americans in Europe, the doubts of our outmanned generals, the cunning of men who hate liberty, all this needs to be heard and ignored. We go forward into empire because, as for my father on Omaha Beach, there is no retreat.

Mr. Batchelor is host of “The John Batchelor Show” on the ABC radio network. The show airs in New York on 770 AM from 10 p.m. to 1 a.m.