Roman Catholicism was feared and hated by many Englishmen for two
distinct reasons. The first was based on bigotry, nourished by memories
of the Marian persecution, the papal bull dethroning Elizabeth, Guy
Fawkes' Plot, and by apprehensions that a Catholic could not be a loyal
subject so long as he recognized the temporal power of the Pope. The
second was political and assumed that Catholicism was the natural
support of absolutism. As Shaftesbury, the leader of the opposition,
stated, popery and slavery went hand in hand. Such fears were deepened
as the general purport of the Treaty of Dover became known.

Into this atmosphere charged with suspicion was interjected the Popish
Plot, said by Titus Oates and his fellow perjurers to be designed to
murder Charles II and place James on the throne. From September 1678,
when Oates began his series of revelations until the end of March 1681,
when the King dissolved at Oxford the third Parliament elected under the
Protestant furore excited by the Plot, Shaftesbury and his followers had
the upper hand. The King was obliged to propose concessions to the
popular will and to offer to agree to limitations on the authority of a
popish successor. But Shaftesbury was bent on passing the Exclusion
Bill, which excluded James from the throne and substituted the King's
illegitimate son, Monmouth. Here he made a fatal blunder because he
alienated churchmen who believed in the divine right of kings, all whose
sense of decency was outraged by the prospect of a bastard's elevation
to the throne, and the supporters of William of Orange, husband of
Mary, the elder daughter of James, and the great opponent of Louis XIV.
Also, when it became obvious that the King would not agree to a change
in the succession, many feared another civil war with all its attendant
dangers of a second military domination. Moreover, the lies of Oates and
his imitators were becoming discredited.