On both the individual and on a larger scale (national, universal), what are the consequences of a lack of tolerance?

I am looking at societal trends, but I am also looking for specific consequences at the individual level. Like have you had any personal experiences with a lack of tolerance? What were they? How did they affect you?

Extrapolating to a societal scale, what happens when thousands or millions of people experience the kind of intolerance you have experienced?