@ Virginia,
One thing about Bryan as Sec'y of State: he resigned in 1915, because he was a strict pacifist and did not want the US to enter WW1.
It's very interesting to speculate what would have happened if the US HAD stayed out. The French probably would have asked Germany for an armistice (there had been widespread mutinies in the French army in 1917, and it is certain that their morale would have fallen even further after Russia made peace with the Germans in the East, freeing up more than a million German troops for action in the West.) If the US had not entered the war at that point, it is quite possible that a peace agreement could have been reached on the basis of status quo ante in the West, with recognition of German gains in the East, in other words, a peace consistent with 'the facts on the ground'.
Had that happened, there would have been no punitive Versailles Treaty, no 'November criminals', no abdication by the Kaiser (except perhaps to have become more of a figurehead constitutional monarch), no significant communist uprisings in Germany, no hyperinflation, Hitler would never have come to power, and hence no WW2 with all its horrors.
On the other hand, had all that happened, my forebears probably would not have left Germany, and I never would have been born to make these speculations. 
