The victims in The Grapes of Wrath are the common people, the people who are at the mercy of the moneyed class. We see this in the fate of the Joads. The Joads are sharecroppers, who lease their land from wealthier landowners. When the depression and dust bowl hit, the land is no longer profitable for sharecropping, so the tenants are kicked out.
Part of their frustration is in their failure to understand the nature of their problem. They do not understand how the land cannot be theirs when they have lived on it for generations. In some cases, they no longer know who owns the land that they are being evicted from. Banks and holding companies are consolidating wealth and financial power, but they are faceless and unapproachable. They also do not understand the environmental situation that has devastated the land. When the dust bowl conditions persist, all they can do is stand and watch the dust swirl and crops wither away.
Much of the victims during the Great Depression were the lower and middle classes, as well as the unemployed and the newly unemployed. As seen in The Grape of Wrathwith the Joad family, a standard American family who has suffered tremendously from the droughts and dust bowl issues that contributed to the Great Depression, they are like many others in that: they struggle finding work and earning a paycheck.
Unfortunately at this time in the Depression, unemployment was at the highest this country has ever seen. This high unemployment rate led to a very low demand for labor, but a giant supply for it as well. This led to very low wages and gruelsome jobs that never paid well. As we see throughout the novel, just to get by and survive, the Joads are forced to take these types of positions. They, and the American people not in the higher class, are the true victims of the Depression.