Europe had been embroiled in the French Revolutionary Wars since 1792. After five years of war, the French Republic subdued the armies of the First Coalition in 1797. A Second Coalition was formed in 1798, but this too was defeated by 1801, leaving Britain the only opponent of the new French Consulate.
From Amiens to the Third Coalition
In March 1802, France and Britain agreed to end hostilities under the Treaty of Amiens. For the first time in ten years all of Europe was at peace. However, many problems persisted between the two sides making implementation of the treaty increasingly difficult. Bonaparte was angry that British troops had not evacuated the island of Malta. The tension only worsened when Bonaparte sent an expeditionary force to re-establish control over Haiti. Prolonged intransigence on these issues led Britain to declare war on France on 18 May 1803. Bonaparte had already revived plans for an invasion of England in March 1803.
Bonaparte's expeditionary army was destroyed by disease in Haiti, and subsequently swayed the First Consul to abandon his plans to rebuild France's New World empire. Without sufficient revenues from sugar colonies in the Caribbean, the vast territory of Louisiana in North America had little value to him. Though Spain had not yet completed the transfer of Louisiana to France per the Third Treaty of San Ildefonso, war between France and Britain was imminent. Out of anger against Spain and having the unique opportunity to sell something that was useless and not truly his yet, Bonaparte decided to sell the entire territory to the United States for a sum total 68 million francs ($15 million). The Louisiana Purchase Treaty was signed on 30 April 1803.
Despite issuing orders that the over 60 million francs were to be spent on the construction of five new canals in France, Bonaparte spent the whole amount on his planned invasion of England.
The nascent Third Coalition came into being in December 1804 when, in exchange for payment, an Anglo-Swedish agreement was signed allowing the British to use Swedish Pomerania as a military base against France (explicitly, the nearby French-occupied Electorate of Hanover, homeland of the British monarch). The Swedish government had broken diplomatic ties with France in early 1804 after the arrest and execution of Louis Antoine, Duke of Enghien, a royalist émigré who had been implicated (on dubious evidence) in an assassination plot against First Consul Bonaparte. The execution of Enghien shocked the aristocrats of Europe, who still remembered the bloodletting of the Revolution and thus lost whatever conditional respect they may have entertained for Bonaparte.
Fanning the flames of the outcry resulting from d'Enghien's death and the growing fear over increasing French power, British Prime Minister William Pitt spent 1804 and 1805 in a flurry of diplomatic activity geared towards forming a new coalition against France. Pitt scored a significant coup by securing a burgeoning rival as an ally. The Baltic was dominated by Russia, something Britain had been uncomfortable with since the area provided valuable commodities like timber, tar, and hemp, crucial supplies to its Royal Navy. Additionally, Britain had supported the Ottoman Empire in resisting Russian incursions towards the Mediterranean. Mutual suspicion between the British and the Russians eased in the face of several French political mistakes, and by April 1805 the two had signed a treaty of alliance.
Meantime, the lull in participating in active military campaigning from 1801–04 permitted Bonaparte to consolidate his political powerbase in France. 1802 saw him proclaimed Consul for Life (his reward for having made peace with Britain, albeit briefly), as well as the establishment of a meritorious order, the Legion of Honour. Then, in May 1804, Bonaparte was proclaimed Napoleon, Emperor of the French and crowned in Notre Dame Cathedral on 2 December 1804. He also created eighteen Marshals of the Empire from among his top generals, securing the allegiance of the army. Napoleon added the crown of (Northern) Italy to his mantle in May 1805, thereby placing a traditional Austrian sphere of influence under his rule (eventually through a viceroy, his stepson Eugène de Beauharnais). Keen on revenge and having been defeated twice in recent memory by France, Austria joined the Third Coalition a few months later.
La Grande Armée at Boulogne
Inspecting the Troops at Boulogne, 15 August 1804
Prior to the formation of the Third Coalition, Napoleon had assembled the Army of England, an invasion force meant to strike at England, from around six camps at Boulogne in Northern France. Although they never set foot on British soil, Napoleon's troops received careful and invaluable training for any possible military operation. Boredom among the troops occasionally set in, but Napoleon paid many visits and conducted lavish parades in order to boost the morale of the soldiers.
The men at Boulogne formed the core for what Napoleon would later call La Grande Armée (The Great Army). At the start, this French army had about 200,000 men organized into seven corps, which were large field units containing about 36 to 40 cannon each and capable of independent action until other corps could arrive to the rescue. On top of these forces, Napoleon created a cavalry reserve of 22,000 organized into two cuirassier divisions, four mounted dragoon divisions, and two divisions of dismounted dragoons and light cavalry, all supported by 24 artillery pieces. By 1805, the Grande Armée had grown to a force of 350,000, was well equipped, well trained, and possessed a competent officer class.
Russian and Austrian armies
The Russian army in 1805 had many characteristics of ancien régime military organization: there was no permanent formation above the regimental level, senior officers were largely recruited from aristocratic circles (including foreigners), and the Russian soldier, in line with 18th-century practice, was regularly beaten and punished to instill discipline. Furthermore, many lower-level officers were poorly trained and had difficulty getting their men to perform the sometimes complex manoeuvres required in a battle. Nevertheless, the Russians did have a fine artillery arm manned by soldiers who regularly fought hard to prevent their pieces from falling into enemy hands.
Archduke Charles, brother of the Austrian Emperor, had started to reform the Austrian army in 1801 by taking away power from the Hofkriegsrat, the military-political council responsible for decision-making in the Austrian armed forces. Charles was Austria's best field commander, but he was unpopular with the royal court and lost much influence when, against his advice, Austria decided to go to war with France. Karl Mack became the new main commander in Austria's army, instituting reforms on the infantry on the eve of war that called for a regiment to be composed of four battalions of four companies rather than the older three battalions of six companies. The sudden change came with no corresponding officer training, and as a result these new units were not led as well as they could have been. Austrian cavalry forces were regarded as the best in Europe, but the detachment of many cavalry units to various infantry formations precluded the hitting power of their massed French counterparts.
Finally, a significant divergence between these two nominal allies is often cited as a cause for disastrous consequences. The Russians were still using the old style Julian calendar, while the Austrians had adopted the new style Gregorian calendar, and by 1805 a difference of 12 days existed between the two systems. Confusion is purported to have ensued from the differing timetables regarding when the Allied forces should combine, leading to an inevitable breakdown in mutual coordination. However, this tale is not supported in a contemporary account from a major-general of the Austrian army, who tells of a joint advance of the Russian and Austrian forces (in which he himself took part) five days before the battle of Austerlitz,
and it is explicitly rejected in Goetz's recent book-length study of the battle.