There are things people do a lot without realizing it. One of those would be shaking hands. For dark skinned people, shaking hands with the white people was forbidden. Some thing like this would get them lynched, because white people were superior and shouldn't interact with "filth".
Public Display of Affection
Black people are not allowed to show affection around whites. Hugs are a bit acceptable, but definitely not kisses and such. To see "trash" interact with one another is already bad for the white. So it's not a surprise that they don't want to see them display their affection.
The Great Depression
The reason the Great Depression even started was because the stock market crashed. 1 out of 4 Americans lost their jobs and homes. As seen in Roll of Thunder with Cassie's dad, many had to travel across the country to find a job. Few people actually owned land, which others sharecropped on. That is also seen in Roll of Thunder, an example being Mr. Granger and people using his land. Black's had to buy used clothes, wearing them to the point where they were threadbare. The Great Depression affected whites too, but a lot of the impact hit dark-skinned people.
The Abolishment of Slavery
The end of slavery was a huge relief for the African Americans. Yet not all white people accepted it fully, and continued to believe that they were superior to the dark skinned. "And now I hereby call upon the people so declared to be free to abstain rom all violence, unless in nesecarry self-defense; and I recommend to them that, in all cases when allowed, they labor faithfully for reasonable wages." Abraham Lincoln. “Even the Northerners who fought the war didn’t really see us equal to white people. So now, even though seventy years have passed since slavery, most white people still think of us as they did then—that we’re not as good as they are—and people like Mr. Simms hold on to that belief harder than some other folks because they have little else to hold on to. For him to believe that he is better than we are makes him think that he’s important, simply because he’s white.” (Taylor, 213)
Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction." -The Thirteenth Amendment to the Constitution of the United States of America
Lynching is when a mob kills someone without a legal trial. It's mostly hanging someone, but lynching include other acts, such as getting tarred. This occurs in Roll of Thunder, Hear My Cry too. A good example is when Mr. Berry is set on fire for "flirting" with a white woman.
“It’s sho’ a shame, all right,” said T.J.’s father, a frail, sickly man with a hacking cough. “These folks gettin’ so bad in here. Heard tell they lynched a boy a few days ago at Crosston.”
Excerpt From: Mildred D. Taylor. “Roll of Thunder, Hear My Cry (Puffin Modern Classics).” Puffin Books, 2016-04-18T11:57:43Z. iBooks.