Where there is a chain of events leading to a loss, which event is the proximate cause?

The most dominant and effective cause, not the nearest cause in time. 

For example, if a ship is scuttled, the proximate cause is the act of scuttling, although the nearest cause in time is seawater entering the ship. An assured who scuttled his ship might claim that a peril of the seas was the cause of his loss, but the insurer would not be liable, since scuttling is wilful misconduct of the assured.