On May 1804, Napoleon made himself Emperor of France, and, functionally though not in name, Emperor of the Italian Republic and the Confederation of Switzerland. With the Holy Roman Empire clearly on its way into the French sphere of influence, Holy Roman Emperor Francis II joined in the name-game and proclaimed himself Emperor of Austria soon after Napoleon's coronation. In 1805, Austria allied with Britain. When the Russian Czar, Alexander I, joined this group in April, the Third Coalition was born. (Prussia, under Frederick William III, stayed out of the coalition.
By 1805, Napoleon was preparing to attack England. He had forces massed on the French coast of the English Channel, and was preparing them for an amphibious assault. The Channel was heavily defended by Nelson's fleet, but England held no sizeable English army to stop Napoleon if his forces got through. Britain breathed a sigh of relief when word came through that a combined Russian and Austrian army was marching on France. Napoleon diverted his army from the invasion of England to handle this new threat, though he continued to put naval pressure on England. On October 21, 1805, the British fleet decimated Napoleon's fleet at the battle of Trafalgar, solidifying its stranglehold on the sea. Two months later, on December 2, 1805, Napoleon solidified his own hold on Europe by smashing the Russo-Austrian offensive in Moravia, at Austerlitz. The Russians retreated to Poland and the Austrians signed the Treaty of Pressburg, which gave Napoleon even more Austrian territory in Italy.
In 1806, Napoleon finally dissolved the tottering Holy Roman Empire, replacing it with the Confederation of the Rhine, with himself as its "protector". Prussia, which had stayed out of the Third Coalition, became concerned with Napoleon's expansion of power in Germany. Frederick William III foolishly went to war without any allies. He was soundly defeated at the battles of Jena and Auerstadt in October 1806 and forced to retreat east to Konigsberg. Along with the Confederation of the Rhine, Napoleon now controlled western Prussia, including Berlin.
Next, Napoleon pursued the Russians, overrunning them at Friedland on June 14, 1807. Alexander I was afraid of retreating into Russia lest a rebellion break out when fighting started on Russian soil. Instead, he negotiated the Treaty of Tilsit with Napoleon in July 1807, allying himself with Napoleon, and horrifying the other rulers in Europe. The Third Coalition was dead.
To add to the prestige of the ceremony, and to add a mark of validation and authority to his imperial status Napoleon invited the Pope to his coronation ceremony, held in the Cathedral of Notre-Dame in Paris. In this action, Napoleon hearkened back to the Pope's crowning of Charlemagne, the great Frankish emperor, in 800 AD. The Pope came to Napoeloen because he did not want to make an enemy, since Napoleon's military power in Italy was steadily increasing, threatening the Papal States and Rome. Although the Pope was present at the ceremony, Napoleon did not allow the Pope to crown him, for to do so might imply a tinge of allegiance or subservience to the Pope. Instead, Napoleon, ever the self-made man, placed the crown of empire on his own head, and then crowned Josephine empress.
Napoleon's planned invasion of Britain in 1805 could have been a disaster for the British. If he could get his forces past the British naval forces and on to the island, which barely had a land army, French control of Britain would be virtually insured. Intervention by Russia and Austria, even though it led to the defeat of both countries, therefore may have saved Britain, preparing the way for Napoleon's later downfall.