World War II
The significance of the Second World War, particularly for America, is hard to overstate. America entered that world-wide war a debtor nation whose economy was still struggling to recover from the Great Depression, with a third rate military whose ability to defend our nation was at best questionable. America came out of that war a creditor nation to the entire world, with global responsibilities and interests heretofore undreamt of, with an undamaged economy that clearly dominated all others, and a military that made it the world’s only nuclear armed Super power. Americans fought in places most could not find on a map prior to this war, which was fought over vast reaches of our Earth on virtually every continent and ocean, and in the skies above them all.
The greatest weapon in any war is the soldier, and America's military services increased in less than four years from 1.4M in 1941, to more than 15M by 1945, the vast majority of them under the age of 26.
The potential of new scientific discoveries exploded during WW2, many of which are still with us today. Radar, electronic computers, mass construction and production techniques, weather prediction, aircraft capable of spanning oceans without stopping including jet powered aircraft, unmanned aerial vehicles including television guidance, remote sensing technologies, rockets capable of reaching outside Earth’s atmosphere and potentially probing outer space, nuclear weapons capable of destroying entire cities with a single bomb – all trace their origins to the pressures of prevailing in a world-wide war.