How might the USA's policy during the 1920's-1930's be seen as a contributory factor in causing the Second World War?

Of course,
the United States policies were not the major contributing factor to the outbreak of .  Instead,
it was the actions of Germany in Europe and Japan in Asia that were the most important factors. 
However, it is possible to argue that the US could have prevented the war from happening (or at
least made it much less likely) if the country had been more assertive and less
isolationist.

We can say...