A conflict is a struggle between opposing forces. Four major types of literary conflict appear in John Steinbeck's novella Of Mice and Men. These conflicts could be labeled person vs. fate, person vs. person, person vs. society and person vs. self. Person vs. fate is revealed in the book's title which comes from the Robert Burns' poem "To a Mouse." The poem suggests that fate often intervenes in the plans "of mice and men" and those plans go astray and are unrealized. In the book, George's, Lennie's and Candy's plan of buying their own "little piece of land" is shattered by fate when Lennie accidentally kills Curley's wife. In fact, Steinbeck imposes a rigid determinism on the character's of the book and none of them are able to break free of their individual fates.
The major person vs. person conflict appears in Chapter Three when Lennie, who has been innocently smiling over the dream of the farm, is challenged and attacked by Curley, who beats Lennie badly, until George gives Lennie the cue to fight. The seeds of the conflict are set up in Chapter Two, when George and Lennie first meet the belligerent boss's son. The conflict is important because it sets up the fury for revenge which overtakes Curley in the book's last two chapters.
Candy and Crooks are characters who struggle against society. Candy is old and unable to work as hard as he did before losing his hand, and so is helpless to the attitudes and prejudices of the other men, especially Carlson, who takes a dislike to Candy's old dog and ends up shooting it when Candy can't do it himself. Crooks is a victim of a society which looks down on his color and race. He is segregated and because of this segregation, deeply lonely.
The major internal conflict (person vs. self) of the book is within George. He loves his friend Lennie, but after the incident in the barn with Curley's wife, George is no longer able to stick up for Lennie. At the end of Chapter Five, he pleads with Curley to leave Lennie alone and not hurt him, but Curley, bent on revenge, will not hear it. Rather than let Lennie fall into the hands of Curley or the Sheriff, something Lennie would never understand, George steals Carlson's gun and shoots his friend. Only Slim seems to understand George's conflict at the end of the book when he tells George, "You hadda George. I swear you hadda."