Scapegoating is the act of placing a person or a specific group of people as the reason for the problem, even though they are not, or at least is not the major reason.
For example, scapegoating has been used in a broad-sweeping way against Nisei's and Issei's, following the bombing of Pearl Harbor, in which people of Japanese descent were assumed to be spies for the Japanese government, while most of them were not. In effect, the usage of scapegoating was to place the blame of the debacle of Pearl Harbor on the Japanese Americans, instead of focusing on the real reason for the debacle, in which the US was heavily unprepared and not on guard for such an attack.
Scapegoating is extremely hurtful against certain communities, but is extremely effective, not only in the usage, but also in the effect that it has.