Final answer:
The greatest decline in foreign trade during the Great Depression was a consequence of the Hawley-Smoot Tariff Act, with U.S. experiencing the most significant increase in unemployment. Britain was least affected due to prior economic conditions.
Step-by-step explanation:
The largest decline in foreign trade during the Great Depression occurred due to the Hawley-Smoot Tariff Act, which raised U.S. tariffs to historically high levels and prompted retaliatory tariffs from other countries, causing world trade to fall by more than forty percent.
The greatest increase in unemployment between 1929 and 1932 occurred in the United States, where the unemployment rate jumped from three percent in 1929 to 25 percent by 1933.
Britain was least affected by the Great Depression comparatively, as it had already been experiencing economic stagnation in the 1920s, so the depression's impact, though still significant, did not represent as sharp a decline.