In Of Mice and Men, why was George forced to kill Lennie?

In short, since you asked several...

1. George is small, square-faced, smarter, and a father-figure. Chapter 1 would give you the best quotes on the 2nd-5th pages of the chapter. Lennie is big, rounder-faced, dumb, childish and mentally slow. He is compared to a bear in the beginning.

2. The setting given in the beginning is on purpose because it is the exact spot that the story ends. The setting in chapter 1 is by a river, more specifically a pool, just off the road on a quiet and serene day.

3. George had to kill Lennie because he would have hurt others again, and had George let someone else kill Lennie, Lennie would have suffered.