War brings great uncertainty especially if it is large. The market would crash if for instance North Korea invaded South Korea or China invaded Japan. If the US invaded Iran on the other hand the market might actually like it after an initial dip as it would force their government to boost spending again.
If productive assets or financial institutions are being blown up then the market looks poorly upon it.
It is too risky a way to boost demand.
Gold would also likely crash as quite simply most assets would be converted back into safer money. Gold could however go up in real terms if governments print money to fund a war. But a war in itself wouldn't really boost gold.
