I'm not a great Hoover admirer but on this issue I'll go to bat for him. In 1929-1933 IOTL you had, first,
very strong & very widespread isolationist sentiment in the US. Second, you had that nasty economic
downturn known as The Great Depression which had the effect(among other things)of making Americans
quite uninterested in problems abroad. These circumstances would have stopped ANY POTUS- as they
indeed stopped Hoover- from doing anything more than uttering strong words. (It should also be kept in mind that then, unlike now, a POTUS did not have virtually unlimited power in foreign affairs, "The Imperial Presidency" being very much a post-Hoover phenomenon). As the noted historian Richard Hofstader commented:
"The historical reputation of any statesman caught between domestic crisis and foreign aggression is
bound to suffer. If Hoover had taken a belligerent stand against Japanese aggression, critics would have been quick to insinuate that he was trying to use friction abroad to distract attention from a crisis at
home."*
*- THE AMERICAN POLITICAL TRADITION, p. 402(continuation of footnote from previous page), of the 1974, Vintage paperbacks edition. First published in 1948. This is a book everyone who is interested in American history should read.