How might a long period of severe heat or cold affect the history of a city or region?

In a long period of severe heat or cold, most of civilians had a really rough time in obtaining foods to feed their families.
Under such conditions, people will have a greater tendency toward violence as a desperate attempt to survive.
Because of this, more wars and rebellions tend to happen within long period of sever cold or heat.

The english language is the primary language of europe