Three times in the last 150 years these re-United States had the opportunity to rule the world--1865, 1945, and 1991.
In the summer of 1865, the War for Southern Independence petered to an end after Lee abandoned Petersburg. At the moment Grant and Lee agreed to the terms by which the Army of Northern Virginia became extinct, the Army and Navy of the United States was the most modern and powerful force on the planet, by far. In fact, the economic power of the United States, and the natural and manpower resources available to it, were beyond peer in the Western World. Noted Civil War author (and Mississippian) Shelby Foote observed that, indeed, the Union fought the war with the Confederacy "with one arm tied behind its back." When Great Britain considered recognizing the Confederacy, Washington's representatives in London warned that if they did so, Great Britain would be the next target after the fall of Richmond.
Frankly, we had a few scores to settle on the other side of the Atlantic. British forces had burned Washington fifty-three years earlier and France had meddled in neighbors' affairs in our hemisphere. We eventually went to war with Spain in 1898 to strip them of possessions in the Caribbean and the Pacific. We could have been the masters of both the Pacific and Atlantic in 1865 or shortly thereafter. But, instead petty politicians kept the re-United States' aggression turned inward and spent the next several decades punishing the southern population of our great nation. The greatest Navy and Army in the Western World was disbanded and the re-United States entered yet another period of self-imposed isolationism--always a sure way to quickly lose the eternal state struggle for preeminence.
Sixty-three years ago, today, the re-United States declared attainment of world preeminence in military, economic, and technological power when a single B-29 bomber (technology for which in itself was unrivaled in the world) dropped an atomic device on an enemy city, and thereby ushered in an era of nuclear nightmare that disturbs our sleep to this day.
Had the re-United States subdued the rest of the world in a few short years following 1865, established an empire governed by the principles of democratic republicanism (little r, little d), one can make the case that the tragic wars of the 20th century might have been prevented. Sure, we would have fought insurgencies against our empire across the globe, but the loss in lives and treasure would have been minuscule in comparison to that wrought by the carnage of what is ironically called the "American Century." Think of the advances such an empire could have made in science and medicine with half of what was spent on building the armies, navies, and air forces (and outrageously expensive nuclear weapon stockpiles) in one century.
And, don't get me started on the opportunities lost in the 90's with the collapse of the Soviet Union!
Sorry, need to put my INTJ personality back in its box and go drive my tractor for awhile.