1.The stock market crash of 1929
2. Bank Failures
3. Reduction of purchasing across the board.
Most isolationists felt that there was no need for americans to feel threatened by developments in Europe and Asia because the vast pacific and atlantic oceans insulated the country from troubles in those regions, and the United States had formed friendly alliances with all the other nations in the Western hemisphere.
The president 2019: Donald Trump
I would argue that John Locke had the most direct influence. Locke believed all men were born a "blank slate" and were shaped by their experiences. The Declaration declares similarly that "All men are created equal".