The United States and the Japanese.
The Stock Market Crash of 1929 occurred during a period of unregulated wealth and excess. On October 14, 1929, investors were selling stock in large amounts. In order to halt the slide in the Dow Jones, the market indicator for the purchase and sale of stocks, Richard Whitney, the Vice President of the Stock Exchange, initiated a plan to purchase large quantities of blue chip stocks, stocks in large and reputable companies. This action resulted in temporarily halting the slide in stocks. The value of the market had increased tenfold in the 1920's as a result of speculation and inflated value in the market. A margin call occurs when value of the account falls below the broker's required minimum. While Whitney invested in the market to halt complete collapse, Charles Merrill of Bank of America suggested that his clients eliminate their financial obligations entirely. He realized that the value of the market was inflated and that the rise in stocks had peaked. The crash itself witnessed a lost of more than $30 billion in value in two days. Both General Electric and General Motors lost more than fifty percent of the value of their stocks during the crash.
Answer: He enforced the Sherman Antitrust Act.
Context/history:
The Sherman Anti-Trust Act was the first measure by Congress to prohibit trusts. It was passed by Congress in 1890. A trust was when stockholders in multiple companies transferred their stock shares to a single group of trustees. Thus a whole industry area could be dominated by a single "trust" organization, destroying the free market of business competition. This was a monopolistic practice which the Sherman Anti-Trust Act ended. Thus the Sherman Anti-Trust Act directly went against the idea of those who believed business success should be based on large business owners colluding with one another.
Initially the Sherman Antitrust Act was not well enforced by US courts. But when Theodore ("Teddy") Roosevelt took office as President in 1901, he pushed enforcement of the Act and worked to reign in the power of big businesses.
Note:
The Clayton Antitrust Act was passed by Congress in 1914, after Teddy Roosevelt was no longer President.
