The main conflict in Of Mice and Men is the struggle for survival in hard times. George and Lennie have nothing in the world but some blankets and three cans of beans. Then have to get jobs at the ranch or die. But George finds it hard to get the Boss to take them on, even though they were sent here from the hiring hall in San Francisco and given bus tickets. The Boss is suspicious of Lennie because he doesn't talk and suspicious of George because he talks too much. George has to put up with a lot of verbal abuse before they get signed on.
Candy and Crooks are also struggling to survive in this heartless environment. Both of them know that their days are numbered. Others see that they have longer futures but that eventually they will end up in the same situations as Candy and Crooks. The men who are capable of working in the fields are driven to exhaustion. Currently they spend their whole days in the hot sun lifting 100-pound sacks of barley onto wagons. It can become excruciating, but still they have to keep on doing it. They work six days a week and probably for ten hours a day. When they get through loading all the existing barley, there will be no further use for them for a while, and they will be sent back on the road looking for something else to do. Meanwhile there are more and more hungry men tramping the road.
The struggle involves competition for jobs. The competition evokes hostility. The hostility leads to outright violence. The men become hard and bitter. Carlson is an example of that. Slim is relatively secure because he is a skilled worker. He can do something that nobody else can do. Young readers should learn from this book that the most important thing in life is survival, and the best way to survive is to have some kind of a marketable skill. There is an old saying:
A useful trade is a mine of gold.
Learn to do something that other people want to have done. The men who suffered the most during the Great Depression were those who were ignorant and unskilled. All they had to offer was their muscles. Muscles are even less marketable today because of the machinery that has been invented to do the hard work, including bulldozers, forklifts, and ditch-diggers. When the unskilled "working stiff" got old and/or handicapped the system had no use for him. There was little protection for such men in those days. It was every man for himself. Steinbeck is implicitly suggesting that there should be a safety net for all Americans, and it should be provided by the federal government--because who else could do it? Steinbeck was one of the many writers who influenced public opinion, which influenced legislation, which led to the protections we all enjoy now.
In his masterpiece The Grapes of Wrath, Steinbeck shows a camp established for migrant workers by the federal government. It seems like paradise in comparison to what the Joads have been living through. It even has flush toilets. When two of the children accidentally flush one of them, they are terrified because they think they have broken it. It has showers and facilities for washing clothes. Unfortunately no family can stay for more than a certain length of time. They have to move on to make way for other migrants, and there are still very few of these clean, hospitable migrant camps.
People who like Of Mice and Men should go on and read other books by Steinbeck, and especially The Grapes of Wrath.