Robert Stewart, Viscount Castlereagh (18 June 1769 - 12 August 1822) was an Anglo-Irish politician who served as Secretary for Ireland from 1798 - 1801, Secretary of State for War from 1807 - 1809 and Foreign Secretary of the United Kingdom from 1812 - 1822. He was responsible for the Act of Union 1800 unifying Britain and Ireland to create the modern United Kingdom and was central to the management of the coalition side of the War of the Sixth Coalition that defeated Napoleon Bonaparte. However, he was widely reviled in Britain and Ireland until his suicide in 1822 due to his support for repressive government measures.
Stewart was elected to Parliament in 1790 as MP for Down. He first rose to prominence by speaking in favour of Prime Minister William Pitt the Younger's Roman Catholic Relief Bill, a failed bill to repeal laws that discriminated against Catholics. His support for Pitt and connections to Charles Pratt, Earl of Camden, allowed him to become advisor to the Lord Lieutenant of Ireland in 1795. He personally led a series of raids in Belfast to arrest leaders of the United Irishmen, a group dedicated to throwing off British rule, and later assumed the role of Acting Secretary of Ireland in 1798. In this capacity he oversaw the defeat of the 1798 rebellion by the United Irishmen and offered clemency to the majority of rebel foot soldiers, choosing to focus on the leadership; however, he earned the nickname "Bloody Castlereagh" due to a number of controversial court-martials of alleged United Irishmen.
In 1799, Castlereagh began lobbying the British Parliament to formally induct Ireland into Britain, creating the modern United Kingdom, in order to guard against French interests and complete the Catholic emancipation process. This was a policy also supported by Pitt, allowing Castlereagh's lobbying to gain traction. Castlereagh lobbied in both the British and Irish parliaments for the Act of Union, winning support in Ireland by promising Catholic emancipation and through careful distribution of titles and peerages. However, while Castlereagh succeeded in pushing the Act of Union through in both Parliaments, opposition from King George III forced he and Pitt to withdraw their commitment to emancipation, enraging the Irish. Further attempts to emancipate were stymied when King George appointed Pitt's enemy Henry Addington Prime Minister, dissolving Pitt's government.
Pitt returned to government in 1804 when the wars against Napoleon Bonaparte resumed, with Castlereagh in the role of Secretary of State for War. Castlereagh, under Pitt and the following Prime Minister William Cavendish-Bentinck, presided over the controversial pre-emptive strike against Copenhagen and the ultimate British defeat in the War of the Fifth Coalition, leading to Napoleon gaining numerous European territories. However, in this position and his following position as Foreign Secretary he oversaw the British victory over Napoleon in the Peninsular War, forcing France to withdraw from the Iberian Peninsular. He also oversaw the war of the Sixth Coalition as Foreign Secretary; it has been argued that Castlereagh was one of those most responsible for victory in the war by keeping the Sixth Coalition together until Napoleon was defeated and forced into exile. Castlereagh negotiated the treaties that ended the war, resisting demands to use them to punish the French in favour of establishing a new political order in Europe. He succeeded in establishing a Congress system where the main powers met and managed European affairs. While this soon collapsed, it led to a long-lasting Conservative order which prevented major conflict between European powers until 1914.
After the slave trade was outlawed in Britain, Castlereagh was placed in charge of eradicating the Atlantic slave trade. He arranged treaties with Portugal, Spain and Denmark forcing them to stop the slave trade; however, when these proved unenforceable he sent the Royal Navy to seize slave ships, including those from other nations. Castlereagh's policies were continued by later governments and eventually succeeded in destroying the Atlantic slave trade.
Reviled at home despite his achievements due to being forced to defend repressive measures taking by the Liverpool government, Castlereagh was publicly vilified by famous bards and poets such as Thomas Moore and Percy Shelley. This, combined with overwork and his being blackmailed for his alleged homosexuality, drove Castlereagh to suffer a nervous breakdown and commit suicide by slitting his throat on 12 August 1822.