What does the term “escalation” refer to?

It refers to a sudden rise in a social setting, emotion, an event, group of people, noise, etc. It is an increase in the intensity of something.

Whereas the Department of Defense is charged with military actions abroad, the Department of Homeland Security works in the civilian sphere to protect the United States within, at, and outside its borders. Its stated goal is to prepare for, prevent, and respond to domestic emergencies, particularly terrorism.