Gunpowder Plot
Robert Catesby led the planning of the conspiracy, which started in May 1604. The people who helped him were either rich Catholics, or gentry families who had a lot of influence.  Catesby may have come up with the plot when he saw that there was little hope that Great Britain would become more tolerant to Roman Catholics, under King James I. Many Catholics were disappointed about the situation. It is more likely though that Catesby simply wanted to give the Catholics in England a chance: The plot was to be the first step of a rebellion. Afterwards,  James' nine-year-old daughter (Princess Elizabeth) could be put in as a Catholic head of state.