Armchair historians love to play these "what if" games, but they are rarely, if ever, revealing. History is just full of too many contingencies to make the kinds of assertions Buchanan does. Here he is on the wonders that would have befallen Europe had the United States avoided World War I:

Without the U.S. government becoming the lender of last resort to finance the war effort ... the Allies would probably have been forced to negotiate an armistice or sue for peace. The kaiser's army, bloodied but undefeated, would have gone home. Germany would have become a fire wall against any drive into Central Europe by a Soviet Russia. ... Lenin, Trotsky, Stalin and the whole grisly gang might have been hung [sic] from the lampposts of Petrograd. A strong, united, and prosperous Germany would not have spawned a Hitler. There might have been no Holocaust, no quarter-century reign of Stalin, no Cold War. [Page 218]

And here he is on the paradise that would have arrived had Britain not defended Poland from Nazi Germany:

Had Britain and France not given the guarantee to Poland, Hitler would almost surely have delivered his first great blow to Stalin's Russia. Britain and France would have had additional years to build up their air forces and armies. ... If the revealed horrors of the Nazis in the East mandated a war, the Allies could have chosen the time and place to strike. Even had Hitler conquered the USSR at enormous cost, would he then have launched a new war against a Western Europe where his ambitions never lay? ... [T]here might have been no Dunkirk, no blitz, no Vichy, no destruction of the Jewish populations of Norway, Denmark, Holland, Belgium, Luxembourg, France, or even Italy. [Page 266]

While seductive, these assertions are so full of qualifications ("might," "probably," "almost surely") and at the time so selective in their consideration of which historical causes to invoke (no discussion of what forces drove Hitler to wage war or to murder Jews, no consideration of the various countries' politics or societies) that they are tantamount to meaningless statements.