The opinion of scientists at Oak Ridge and the University of Chicago about the use of nuclear weapons were concerned about how nuclear bombs might be used in World War II. They discussed the future of atomic energy and its political implications recommending that such bombs should not be used against Japan “unless the terms which will be imposed upon Japan have been made public in detail and Japan knowing these terms has refused to surrender.”
Were intent on invading north America
The answer to your question, "What foreign policy did the Tokugawa practice", it would be isolationism. Isolationism is a type of foreign policy that was created by leaders who wants to protect their country's best interests. They also keep their connections at a distance.
The main issue was that they had no ways of reaching the North American continent en mass. They never developed a great naval army and this mean that they didn't have many ships that could transport armies and colonists so they couldn't really establish themselves as a great nation in the New World. They did have some parts, but it was insignificant compared to Spain and England.
Do you mean during the time in Great Depression? if so, is due to the state of US. It was the largest producer and creditor in the world after WWI. It lent money to Britain and France to help them recover their economies and helped Germany pay its war indemnity. In addition, many other countries depended on the US as a major market for their products. As a result, US played a leading role in the economic development of the world.
Sadly, someone shared a rumour of stock shares that there would soon be a recession. US was in panic and many sold their shares leading to the decrease in economy, which affected every other country, especially European countries and Germany, whom had to pay the indemnity and pay the loan.