The Gordon Riots of 1780 began as an anti-Catholic protest in London against the Papists Act of 1778, which was intended to reduce official discrimination against British Catholics. The protest evolved into riots and looting.
The Popery Act 1698 had imposed a number of penalties and disabilities on Roman Catholics in England; the 1778 Act eliminated some of these. An initial peaceful protest led on to widespread rioting and looting and was the most destructive in the history of London. Painted on the wall of Newgate prison was the proclamation that the inmates had been freed by the authority of "His Majesty, King Mob". The term "King Mob" afterwards denoted an unruly and fearsome proletariat.
The Riots came at the height of the American War of Independence, when Britain was fighting American rebels, France, Spain and the Dutch Republic. They led to unfounded fears that the riots had been a deliberate attempt by France and Spain to destabilise Britain before an imminent invasion similar to the Armada of 1779.
The stated intention of the Papists Act of 1778 was, as its preamble notes, to mitigate some of the official discrimination against Roman Catholics in the Kingdom of Great Britain. It absolved Catholics from taking the religious oath when joining the British Armed Forces as well as granting a few and limited liberties. There were strong expedient reasons for this change. British military forces at the time were stretched very thinly in what had become a global American War of Independence, with conflicts ongoing with France, Spain, and the new United States. The recruitment of Catholic people would be a significant help to address this shortfall of manpower.