In 1805 the Austrian Empire was only a year old, having been founded from the remnants of the far larger Holy Roman Empire. It was founded by the Habsburg Emperor Francis II (Francis I of Austria) in reaction to Napoleon's proclamation of the First French Empire in 1804. After Prussia succumbed to Napoleon in 1795, Austria bore the brunt of France's expansion eastward. This put enormous strain on the Austrian economy, and meant that by 1805 the war with France was extremely unpopular within the country.
Emperor Francis I was in a difficult position: on one hand he recognised the threat posed by Napoleonic France, but on the other, he did not want to antagonise his own hard-pressed people. To balance these opposing problems, in 1804 Francis I entered into a secret pact of military cooperation with Alexander I, proposing war privately whilst declaring that he had no intention of doing so in public. Eventually, Austrian reluctance to join the war in 1805 was overcome by financial aid sent from the British Empire.