@OmSigDAVID,
First of all there is a tradition of having bonfires between the Autumn Equinox and the Winter Solstice. This dates back to Pagan times, and deals with the notion of feeding the Sun, as it gets weaker. There's also the practicalities of clearing up the dead wood after harvest.
The 5th November in particular deals with the Gunpowder plot. A group of Catholic conspirators tried to blow up the Houses Of Parliament and kill James I who was due to address Parliament at the time. The most celebrated conspirator was Guido (Guy) Fawkes. The plot failed, and we celebrate the failure of one of History's most audacious terrorist plots, by burning an effigy of Guy Fawkes (or a popular hate figure) and setting off a load of fireworks.
Remember remember the fifth of November
With gunpowder treason and plot.
I see no reason why gunpowder season,
Should ever be forgot.