Effects of Marshall becoming president upon Wilson's stroke being fatal in 1919:
(1) The US will probably join the League of Nations, but the importance of this can be exaggerated. As I posted here last year:
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But the hard-core opponents of
any League (the so-called Irreconcilables) were a minority within the Republican Party. Most Republicans were willing to accept the League if Wilson agreed to the Lodge Reservations. Now you might say that if Marshall agreed to the Lodge Reservations, the Republicans would just present new demands. But in view of widespread public support for some sort of League, and the likely popular perception that Wilson had been "martyred" in the fight for the League, I just don't think they could get away with that, and plenty of Republicans would break ranks with Lodge if he tried that.
Even if you say that Lodge always wanted to kill the League, that his proposed reservations were just a ploy, the very fact that Lodge did not openly oppose the League per se meant that he recognized the
idea of a League (which after all Theodore Roosevelt and William Howard Taft had both supported) was popular, even among people who had doubts about Wilson's version.
As I have posted in soc.history.what-if about Lodge's decision to insist on reservations rather than to oppose ratification outright:
"This involved an element of risk, since theoretically Wilson might accept the reservations (and once that happened, Britain and France would accept that having the US go into the League with reservations was better than having it not go in at all). Senator James Watson (R-Indiana) in his *As I Knew Them* recalled how he had actually raised this point with Lodge:
"'Senator, suppose that the President accepts the Treaty with your reservations. Then we are in the League, and once in, our reservations become purely fiction.' (Watson, like Borah and other irreconcilable opponents of the League, thought that declaring that the US was not bound by Article X unless Congress decided on the use of force would not amount to much. Once the League's Council had voted to use force, with the US delegate agreeing, Congress, he thought, would not dare refuse; to turn down a President's request under such circumstances would greatly embarrass the US before the world.)
"Lodge was not worried, replying with a smile, 'But my dear James, you do not take into consideration the hatred that Woodrow Wilson has for me personally. Never under any set of circumstances in this world could he be induced to accept a treaty with Lodge reservations appended to it.'
"'But,' Watson retorted, 'that seems to me to be a slender thread on which to hang so great a cause.'
"'A slender thread!' Lodge exclaimed. 'Why, it is as strong as any cable with strands wired and twisted together.'
"Lodge was right--yet in a sense Watson was right, too. There *was* a slender thread--Wilson's life. Wilson would never have accepted the Lodge Reservations, but what if his stroke had killed him? Then the much more flexible Thomas Marshall would have become President, and the combination of Wilson's 'martyrdom' and Marshall's willingness to accept the Lodge Reservations (or at least something like them) could have made US membership in the League inevitable."
http://groups.google.com/group/soc.history.what-if/msg/71c89de9983668a3
Would formal membership in the League have made much difference? I doubt it. The US did informally cooperate with the League, for example, in the Manchurian crisis of 1931. Granted, it went no further than moral disapproval and a refusal to recognize Manchukuo, but that is probably as far as it would have gone as a member of the League, too.
Again I'll quote an old soc.history.what-if post of mine:
"I do not think that joining the League would have affected the basic fact of American public opinion during the 1930's: that most people thought that it was a mistake for the U.S. to have joined the Great War, didn't want it to happen again, and were worried that League sanctions would lead to another war. Remember all the nations that *did* join the League and then helped appease Germany, Italy, and Japan anyway. I don't think the U.S. would have been any different.
"Also note that, for example, if the question arose of economic sanctions on Italy for its invasion of Ethiopia, the U.S. government, even as a member of the League, would surely take into account the existence of a large Italian-American vote. German-Americans were even more numerous, and while they were more 'assimilated' than in 1914-18 and less enthusiastic about Hitler than about the Kaiser, they were still far from eager for a war with the Fatherland, or for sanctions that might lead to war. Note the comment made by the American diplomat Joseph Grew in his diary in 1924: 'Every position he [an American member of the League's Council or Assembly] might take with regard to European politics would infuriate some national element at home, the Italians or the Irish, the Germans, Poles, or Jews. This is the real and practical reason for our not joining.' Quoted in Richard W. Leopold, _The Growth of American Foreign Policy_, p. 454."
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(2) One interesting difference Marshall could make:
"Vice-President Thomas R. Marshall was reported in the New York Times of April 21, 1919, to the effect that he 'would send a sufficiently large force to Russia to thoroughly exterminate the Bolsheviki.'" Evans Clark, *Facts and Fabrications about Soviet Russia*
http://books.google.com/books?id=po0bAAAAMAAJ&pg=PA14 (Clark's book is a pro-Bolshevik polemic, but the same quote is found in Charles Marion Thomas, *Thomas Riley Marshall, Hoosier Statesman,* p. 252.)
Does he try to carry out that policy in this ATL? I think that by the time Wilson suffered his stroke in OTL, it was probably too late for the US to save the Whites. Also note that Marshall made his statement in April, when the temporary success of Kolchak's Spring Offensive led many people in the West to overrate his chances of success.
(3) The Republicans are still going to win the presidency in 1920. There was just too much dissatisfaction with the Democrats. First, there was dissatisfaction with the war itself. The dissatisfaction was not just among people who opposed the declaration of war in 1917 (though many people, especially German-Americans, did). With others, as one observer said, "It was not exactly a feeling that we should or could have kept out of the war, but rather, an annoyed feeling that the war should somehow have avoided us." Second, even if the Versailles Treaty is ratified by the Senate, there will be plenty of dissatisfaction with it--by German-Americans feeling it was much too harsh on Germany, Italian-Americans thinking Italy didn't get enough, Irish-Americans who will object that it provided for an independent Poland and an independent Czechoslovakia but not an independent Ireland, idealistic liberals upset by the "betrayal" of China over Shantung, etc. Third, there will be dissatisfaction with the economic situation--"profiteers," inflation followed by deflation in 1920, etc. Related to that will be dissatisfaction with the taxation and government interference in the economy that come naturally with a major war.