Of Mice and Men is set in the 1930s of the Great Depression. Men like George and Lennie are working for low wages:
The agricultural scene in California in the 1930s, particularly in Salinas Valley, was dominated by large collective farms, or "farm factories," owned by big landowners and banks. These farm factories employed hundreds of workers, many of whom were migrants.
The economical situation caused deep depression for those involved. George and Lennie move from ranch to ranch, trying to get ahead. They live a lonely life, having no place to call home. They only dream of the day they can buy their own farm and plant roots:
Small farms of a few hundred acres, such as the one Lennie and George dream about, were relatively scarce. On the large farms, low wages for picking fruit and vegetables often led to economic unrest. In September 1936, thousands of lettuce workers in the Salinas Valley went on strike over low wages. The situation grew tense, and an army officer was brought in to lead vigilantes against the strikers. The strike was crushed within a month. Steinbeck covered the strike as a reporter for the San Francisco News.
During this time, loneliness is a recurrent them. George admits that he leads a lonely life, claiming that living from ranch to ranch brings about a lonely existence. Even though Lennie frustrates George, he admits that life would be much lonelier without him:
George had promised Lennie's aunt that he would look out for Lennie, and although George complains about having to take care of him, their friendship gives George someone with whom he can share his dream.
Living the migratory life is indeed lonely. Since Lennie is always getting into trouble, he and George are constantly on the move. George states that the life he lives is indeed a lonely one:
Loneliness is a recurrent theme in the novel. "Guys like us," George says, "that work on the ranches, are the loneliest guys in the world. They got no family. They don't belong no place." Lennie replies: "But not us. And why. Because . . . because I got you to look after me, and you got me to look' after you, and that's why."
No doubt, shooting Lennie was the most difficult decision George had ever had to make. He lost his companion and friend. He lost his will to dream.