The 19th century

Union with Ireland: The second stage in the development of the United Kingdom took effect on January, 1st, 1801, when the Kingdom of Great Britain merged with the Kingdom of Ireland to form the United Kingdom of Great Britain and Ireland.

The legislative union of Great Britain and Ireland was completed under the Act of Union 1800. The country's name was changed to "United Kingdom of Great Britain and Ireland". The Act was passed in the British and therefore unrepresentative Irish Parliament with substantial majorities achieved in part (according to contemporary documents) through bribery, namely the awarding of peerages and honors to critics to get their votes. The separate Parliaments of Great Britain and Ireland were abolished, and replaced by a united Parliament of the United Kingdom. Ireland thus became part of an extended United Kingdom. Ireland sent around 100 MPs to the House of Commons at Westminster and 28 peers to the House of Lords.

Napoleonic wars: During the War of the Second Coalition (1799–1801), Britain occupied most of the French and Dutch colonies (the Netherlands had been a satellite of France since 1796), but tropical diseases claimed the lives of over 40,000 troops. When the Treaty of Amiens ended the war, Britain was forced to return most of the colonies. The peace settlement was in effect only a cease fire, and Napoleon continued to provoke the British by attempting a trade embargo on the country and by occupying the German city of Hanover (a fief of the British crown). In May 1803, war was declared again. Napoleon's plans to invade Britain failed due to the inferiority of his navy, and in 1805, Lord Nelson's fleet decisively defeated the French and Spanish at Trafalgar, which was the last significant naval action of the Napoleonic Wars.

All the participants in the Napoleonic Wars.

Blue: The Coalition and their colonies and allies. 

Green: The First French Empire, its protectorates and colonies, and allies.

In 1806, Napoleon issued the series of Berlin Decrees, which brought into effect the Continental System. This policy aimed to eliminate the threat of the United Kingdom by closing French-controlled territory to its trade. The United Kingdom's army remained a minimal threat to France; the UK maintained a standing army of just 220,000 at the height of the Napoleonic Wars, whereas France's army exceeded a million men in addition to the armies of numerous allies and several hundred thousand national guardsmen that Napoleon could draft into the military if necessary. Although the Royal Navy effectively disrupted France's extra-continental trade, both by seizing and threatening French shipping and by seizing French colonial possessions, it could do nothing about France's trade with the major continental economies and posed little threat to French territory in Europe. In addition, France's population and agricultural capacity far outstripped that of the United Kingdom.

Many in the French government believed that cutting the United Kingdom off from the Continent would end its economic influence over Europe and isolate it. Though the French designed the Continental System to achieve this, it never succeeded in its objective. The United Kingdom possessed the greatest industrial capacity in Europe, and its mastery of the seas allowed it to build up considerable economic strength through trade to its possessions from its rapidly expanding new Empire. Britain's naval supremacy meant that France could never enjoy the peace necessary to consolidate its control over Europe, and it could threaten neither the United Kingdom nor British colonies outside the continent.

The Spanish uprising in 1808 at last permitted Britain to gain a foothold on the Continent. The Duke of Wellington and his army of British and Portuguese gradually pushed the French out of Spain and in early 1814, as Napoleon was being driven back in the east by the Prussians, Austrians, and Russians, Wellington invaded southern France. After Napoleon's surrender and exile to the island of Elba, peace appeared to have returned, but when he escaped back into France in 1815, the British and their allies had to fight him again. The armies of Wellington and Von Blucher defeated Napoleon once and for all at Waterloo.

Simultaneous with the Napoleonic Wars, trade disputes and British impressment of American sailors led to the War of 1812 with the United States. A central event in American history, it was little noticed in Britain, where all attention was focused on the struggle with France. The British could devote few resources to the conflict until the fall of Napoleon in 1814. American frigates also inflicted a series of embarrassing defeats on the British navy, which was short on manpower due to the conflict in Europe. A stepped-up war effort that year brought about some successes such as the burning of Washington D.C., but many influential voices such as the Duke of Wellington argued that an outright victory over the US was impossible.

Peace was agreed to at the end of 1814, but not before Andrew Jackson, unaware of this, won a great victory over the British at the Battle of New Orleans in January 1815 (news took several weeks to cross the Atlantic before the advent of steam ships). The Treaty of Ghent subsequently ended the war. As a result, the Red River Basin was ceded to the US, and the Canadian border (now fixed at the 49th parallel) completely demilitarized by both countries, although fears of an American conquest of Canada persisted through the 19th century.

George IV and William IV: Britain emerged from the Napoleonic Wars a very different country than it had been in 1793. As industrialization progressed, society changed, becoming more urban and less rural. The postwar period saw an economic slump, and poor harvests and inflation caused widespread social unrest. Europe after 1815 was on guard against a return of Jacobinism, and even liberal Britain saw the passage of the Six Acts in 1819, which proscribed radical activities. By the end of the 1820s, along with a general economic recovery, many of these repressive laws were repealed and in 1828 new legislation guaranteed the civil rights of religious dissenters.

A weak ruler as regent (1811–20) and king (1820–30), George IV let his ministers take full charge of government affairs, playing a far lesser role than his father, George III. The principle now became established that the king accepts as prime minister the person who wins a majority in the House of Commons, whether the king personally favors him or not. His governments, with little help from the king, presided over victory in the Napoleonic Wars, negotiated the peace settlement, and attempted to deal with the social and economic malaise that followed. His brother William IV ruled (1830–37), but was little involved in politics. His reign saw several reforms: the poor law was updated, child labor restricted, slavery abolished in nearly all the British Empire, and, most important, the Reform Act 1832 refashioned the British electoral system.

There were no major wars until the Crimean War of 1853-56. While Prussia, Austria, and Russia, as absolute monarchies, tried to suppress liberalism wherever it might occur, the British came to terms with new ideas. Britain intervened in Portugal in 1826 to defend a constitutional government there and recognizing the independence of Spain's American colonies in 1824. British merchants and financiers, and later railway builders, played major roles in the economies of most Latin American nations. The British intervened in 1827 on the side of the Greeks, who had been waging a war of independence against the Ottoman Empire since 1824.

Whig reforms of the 1830s: The Whig Party recovered its strength and unity by supporting moral reforms, especially the reform of the electoral system, the abolition of slavery and emancipation of the Catholics. Catholic emancipation was secured in the Catholic Relief Act of 1829, which removed the most substantial restrictions on Roman Catholics in Britain.

The Whigs became champions of Parliamentary reform. They made Lord Grey prime minister 1830–1834, and the Reform Act of 1832 became their signature measure. It broadened the franchise and ended the system of "rotten borough" and "pocket boroughs" (where elections were controlled by powerful families), and instead redistributed power on the basis of population. It added 217,000 voters to an electorate of 435,000 in England and Wales. The main effect of the act was to weaken the power of the landed gentry, and enlarge the power of the professional and business middle-class, which now for the first time had a significant voice in Parliament. However, the great majority of manual workers, clerks, and farmers did not have enough property to qualify to vote. The aristocracy continued to dominate the government, the Army and Royal Navy, and high society. After parliamentary investigations demonstrated the horrors of child labor, limited reforms were passed in 1833.

Chartism emerged after the 1832 Reform Bill failed to give the vote to the working class. Activists denounced the 'betrayal' of the working class and the 'sacrificing' of their 'interests' by the 'misconduct' of the government. In 1838, Charists issued the People's Charter demanding manhood suffrage, equal sized election districts, voting by ballots, payment of MPs (so poor men could serve), annual Parliaments, and abolition of property requirements. Elites saw the movement as pathological, so the Chartists were unable to force serious constitutional debate. Historians see Chartism as both a continuation of the 18th century fight against corruption and as a new stage in demands for democracy in an industrial society.

In 1832 Parliament abolished slavery in the Empire with the Slavery Abolition Act 1833. The government purchased the slaves for £20,000,000 (the money went to rich plantation owners who mostly lived in England), and freed the slaves, especially those in the Caribbean sugar islands.