While trying to break through to the Master Cultivation Level, the previous Maxwell Family Head failed and suffered large backlash, weakening him greatly and making it so that he would be unable to unleash the full power that he once had.
The Maxwell Family tried to keep it secret, but word got out and after the Lin Family Head received it and verified it, a formal declaration of war was sent to the Maxwell Family, Epstein Family and Sentinels Faction.
A war between such large cultivation families and large groups of cultivators could decimate the entire city, so in the declaration of war, the Lin Family set a time and a place for them to face each other in a direct confrontation.
If they do not wish to battle, they may submit or expect an all-out attack within the city, which would cause great destruction and unnecessary death, and may even alert powerful cultivators that they didn't wish to mess with.