The most important factor from the options that lead to radicalized political parties was The Great Depression of 1929 (C).
The Wall Street Crash of 1929 led to a chain reaction not only in the U.S. but in many European countries as well. In the worst moments of the period, 22 to 23% of the American workforce, and 44% of German's workforce didn't have a job.
Due to the crisis, many American creditors charged loans made throughout the world; American companies stopped investing in other countries.
This generalized crisis, unemployment, and increasing misery of the population created a fertile soil on which fascist and nazi political figures fed.
