ELI5: Why is growling such a common way to show aggression in the animal kingdom?

Growling in dogs isn’t a show of aggression. It is a show of unease - you’re invading its space or you represent a threat and (s)he wants you to back off.

It’s actually a sign the dog would prefer for this to not evolve into conflict.
Aggressive dogs attack without any growling.

Explain Like I`m Five: good questions, best answers.