According to the Encyclopaedia Britannica, Napoleon Bonaparte spread nationalism in England by changing the balance of power in Europe and the rest of the world. Though the defeat of Napoleon was affected by an alliance of countries, England received primary credit for the victory. This enabled England to become the dominating force in Europe and a large portion of the rest of the world in the coming years.
During the Napoleonic Wars, England was forced to fight not only on the European front, but also in other parts of the world, such as Egypt, India, the West Indies, South Africa and the United States. This ongoing conflict served to strengthen the British army. Before the 23 years of warfare with Napoleon, it numbered barely 40,000 men, but at the height of the war, the British army had grown to a fighting force of more than 250,000. When Napoleon was defeated, England retained an overwhelming military presence. This enabled England to embark upon a program of imperial expansion that vastly increased its colonial power.
Encyclopaedia Britannica points out that the end of the conflict with Napoleon also brought about reforms at home in England. The state became more decentralized, leaving more rights in the hands of self-governing citizens. Though the central government was still powerful and not a real democracy, this growing liberality gave "free-born Englishmen" greater participation in decisions concerning the economy and society. All this led to a greater sense of British nationalism.