What Mars does in a chart
Mars is the part of the chart that answers one question:How do I go after what I want? It describes drive and desire — not events, and not outcomes.
What Aquarius does to it
Aquarius is a air sign, so it moves on ideas and conversation. It is also fixed, which means it holds things. Put those together with Mars and you get acts on principle — independent, systemic, odd-angled, applied specifically to drive and desire.
Aquarius is ruled by Uranus, so this placement tends to be coloured by independence as well.
The useful version
Placements are not verdicts. This one describes a default setting, not a limit — the things listed above are what you do when you are not thinking about it, which is exactly why noticing them is worth something.