<p>So essentially does margin collapsing occur when you don't set any margin or padding or border to a given div element?</p>

"the expression collapsing margins means that adjoining margins (no non-empty content, padding or border areas or clearance separate them) of two or more boxes (which may be next to one another or nested) combine to form a single margin."
Source:
Box Model - 8.3.1 Collapsing margins