We still do not know precisely what the Gunpowder plotters hoped to achieve by destroying Parliament in 1605. They were Catholics and there had recently been a major clampdown on that faith, so they presumably hoped to strike a blow in retaliation.
It is possible they wanted a Catholic monarch to replace King James I, who had been crowned in 1603, though such a violent terrorist plot was unlikely to gain support for a Catholic king.
A controlled experiment in 2005 – to mark the 400th anniversary of the plot – showed that the amount of gunpowder Guy Fawkes smuggled into Parliament could easily have destroyed the House of Lords, and killed everyone in it, including the King, the entire political class and the leadership of the Church.
This would have created a huge and dangerous vacuum, which could have, in turn, led to a bitter power struggle. It is not fanciful to believe that this could have caused civil war and foreign invasion – the Spanish, French and Scots could all have seized the opportunity to intervene.
With memories of the Spanish Armada only 17 years earlier still fresh, it’s no wonder that people celebrated so vociferously when Fawkes was found out and the plot foiled.