Researchers depend on whatever information has been left behind by the event. Archaeologists check the information for accuracy using secondary data sources.
Original sources are all first accounts of history recorded by a living individual on the basis of an occurrence. Secondary data sources are recorded descriptions of historically based upon primary evidence.
I think the answer is Urban Sprawl, because when that happens, trees are cut down to make room for cities/towns, and when trees are cut down there is less of a chance for wildfires.
