The nominal casus belli for Britain's entry into the French Revolutionary and Napoleonic wars was the execution of the French king Louis XVI in 1793. The execution of the French monarch shocked European public opinion and Britain was no exception. Newspaper accounts and surviving diaries record instances of public outrage and mourning for Louis XVI, and this public sentiment gave added impetus to the war party inside the British government. The British government had prior to the execution dispatched the Foreign Secretary William Grenville to the National Convention to gain guarantees for the Low Countries' neutrality, but such attempts to defuse the deterioration in Franco-British relations were futile. After the execution, Prime Minister Pitt expelled the French ambassador and pushed for militia bills to put Britain on a war footing. The French National Convention responded to Pitt's action by declaring war on Britain.

However, the sympathy over Louis XVI's execution was reflective of broader currents and eddies inside the British body politic. Although the somewhat Whiggish historiography of the Victorian era had a tendency to portray British society as aloof from revolutionary activism of the 1780s, social historians from the 1960s onward have noted that British society was increasingly polarized and these divisions were quite sharp. The social leveling potential of the French Revolution encouraged radical groups like the London Corresponding Society and other intellectuals like Thomas Paine, whose English-language pamphlets circulated through groups like the LCS. Additionally, economic grievances and other class conflicts were percolating within the British isles. The violent turn of the French Revolution and tales of mob action helped to mobilize various conservative and royalist factions within Britain. The presence of French noble emigres and other refugees within Britain also encouraged this anti-Revolutionary sentiment by both spreading tales of Revolutionary excesses and by virtue of their very presence as foreigners, which stoked fears of espionage and that French refugees were displacing Britons in trades like milliners or service. The execution of Louis XVI gave the disparate forces arrayed against the Revolution a political martyr to rally around and British belligerency also witnessed a stiffer regime of domestic political repression and the suppression of alleged "Jacobin" societies like the LCS.

In some ways the question "why did Britain remain in the Napoleonic Wars?" is more fruitful than why it joined hostilities in the first place. Britain's early reversals in the Low Countries and Toulon were damaging blows for a government that hoped the war would be short. The Flanders campaign in particular revealed the shortcomings of the British Army and the scapegoating of the Duke of York for the systemic failures added fuel to the suppressed radical press. The success of French arms on the continent also meant that Britain had to fight through proxies or take advantage of circumstances. But the war put the British government on the horns of dilemma. War finance via ever escalating debt put the British exchequer in a precarious position and to give up without any gain put any government at dire risk of being charged with bankrupting the nation for little to show for it. There was also a fear within the British ruling establishment that leaving the war at an inopportune time would only encourage a revolution within the British isles. The Spithead and Nore Mutinies of 1797 was a major crisis for two months and although diffused by concessions on the part of the government towards seamen's pay, a number took it as a sign that Jacobinism was taking root in Britain. War with France invariably led to troubles in Ireland and Wolfe Tone's 1798 rebellion led to the suspension of habeas corpus and renewed fears within the British government of a disloyal population.

One of the main priorities for the British government in the 1790s and early 1800s was to find a way to extricate themselves from the war in a safe manner. British naval superiority, which only grew as the French fleet atrophied in port, proved to be a boon for the prestige of the British government in that embarrassments on land like the Flanders campaign could be offset by successes like the Glorious First of June. Naval power also allowed Britain to extend the war globally towards European colonial possessions, albeit with only a measure of mixed success. The vast infrastructure needed to support such an unprecedented naval effort also meant there was a sizable segment of the British economy devoted to support the war, and while the war depressed many parts of the British economy, some elements of the mercantile community did thrive under military contracts. What this meant was that there was little traction an immediate peace party could make inside the wartime British system as it became a given within many political circles that Britain would accept an honorable peace with France if given the opportunity.

The problem for this sanguine hope for an honorable peace was that Britain lacked a willing French partner. The failures of the early Revolutionary armies hardened extremist sentiments against compromise while the later successes of the Directory's troops encouraged intermingled dreams of exporting both the Revolution and French power beyond the borders of Bourbon France. There was hope among many Britons that the Peace of Amiens signed with Napoleon in 1802 would lead to a lasting accord, but such dreams proved short-lived. Napoleon's reordering of European affairs coupled with his keeping the French army on a wartime footing alarmed many within Britain such as Charles James Fox, who as opposition leader in the House of Commons had been one of the more vocal critics of the French war. Fox's tour of France in 1803 left him very much disenchanted with both the peace and Napoleon. The British government was not blameless in the failure of Amiens as it flaunted its non-compliance with provisions like the evacuation of Malta, and the other European powers also entered into peace with France somewhat half-heartedly. Nevertheless, a good deal of the onus for the breakdown of Amiens lay with Napoleon. Even though Amiens recognized French hegemony on the continent, Napoleon still extended French power over its satellite states in the Low Countries, Switzerland, and northern Italy, which radically destabilized the European balance of power and engendered a war party within Britain to end the peace. Even though the Wars of the Third and Fourth Coalitions ended in French victory, diplomats became trapped into continued war. British peace feelers after his victories of Austerlitz and Friedland often ran afoul of the great power politics of France and Russia. Napoleon sent out disingenuous peace feelers to Britain, but with the caveat of Russian mediation which after Tilsit had a pro-French tilt. Instead of peace, Napoleon preferred to use his unprecedented hegemony to lock Britain out of the continent, a process that led to the expansion of French power throughout the continent.

This expansion of Napoleon's empire not only shored up domestic support for the war in Britain, but it also afforded British arms and money the opportunity to make themselves felt on the continent, whether in the Iberian peninsula or via great power proxies like Austria and later Russia. French imperial expansion practically guaranteed a political reaction against Napoleon, rendering the common defense of Napoleon- that he did not initiate the majority of the Napoleonic wars- somewhat moot; accepting French hegemony entailed a significant loss of state sovereignty and political power, which was a cross neither Austria nor Russia were willing to bear.

British naval supremacy meant that it was insulated against the best card Napoleon possessed, his mastery of the battlefield, and ensured that Britain could fight the Napoleonic Wars with relatively little risk. British defeats like the retreat from Corunna and the subsequent abandonment of central Spain could not lead to the Imperial Guard marching in London. The result was that Britain's involvement in the war became quite protracted and sometimes a quite remote affair inside the British isles. For example, even though Jane Austen wrote her early novels during wartime, the wars only appear tangentially in her sharply drawn portraits of Regency society. The very length of the wars meant that good portion of the rankers of the British army at Waterloo were either children or had not even been born when Louis XVI was executed, which kick-started the whole affair to begin with.

Sources

Linch, Kevin. Britain and Wellington's Army: Recruitment, Society and Tradition, 1807-15. Houndmills, Basingstoke, Hampshire: Palgrave Macmillan, 2011.

Muir, Rory. Britain and the Defeat of Napoleon, 1807-1815. New Haven: Yale University Press, 1996.

Uglow, Jennifer S. In These Times: Living in Britain Through Napoleon's Wars, 1793-1815. New York : Farrar, Straus and Giroux, 2014.