You Can Blame Taft

There is a theory that says that all of the blood of the 20th century can be laid at the feet of William Howard Taft.
The 1912 Presidential election began with Theodore Roosevelt's displeasure with Taft, his chosen successor. The Republican convention for the nomination that year was prepared to go for Roosevelt; Taft's supporters effectively kept them out of the hall, ensuring that TR would be cut out of the process. Roosevelt bolted the convention and began his own, third-party candidacy. Had Taft bowed out of the 1912 election in favor of the much more popular Roosevelt, TR would easily have beaten Wilson in a two-man race and with an unsplit Republican party. Having TR in charge might well have either seen a diplomatic answer to European tensions leading to WWI, or a lessened war itself due to his early and vigorous entry of the USA into the thick of it. Come War's end, he would never  have been drawn into the treaties that forced the economic strangulation of Germany, which would have denied Hitler the unrest he needed to build wounded German Nationalism into National Socialism. It also might well have prevented the toppling of the Tzar because the severe difficulties that led to the Russian Revolution might have been averted with a shortened WWI. No crushed Germany, no Hitler. No Hitler, no Final Solution, no Holocaust. Also no Cold war, no Mao Zedong, no WWII, no Lenin, no Soviet Union, probably no Korea or Vietnam. Not to mention no misguided Prohibition and the resulting rise of organized crime - maybe even the saved lives of millions who died in the 1917 influenza epidemic, spread rapidly by the soldiers of the Great War.
Taft insisted on running. Woodrow Wilson inevitably carried the election due to the split Republican party (Roosevelt ran second - the highest vote count of any third-party candidate, ever). Wilson waited to enter WWI until his second term, carrying out a policy of isolationism until the soils of Europe were saturated with blood.  The Treaty of Versailles ending WWI carved up Europe along lines that bred hatred, anger and resentment. War reparations forced on Germany guaranteed the poverty of German citizens, ripening them for the appeals of a man telling them they were the chosen, the wronged, the Master Race.
TR proved throughout his Presidency that he had the right stuff to steer the global conflicts of the nineteens away from disaster. He was the first President to think and act globally, and won the Nobel Prize for his flawless mediation of the Russo-Japanese War.
It is interesting to consider that it might have been a very different 20th century.