The Napoleonic Wars brought great changes both to Europe and the Americas. Napoleon had succeeded in bringing most of Western Europe under one rule—a feat that had not been accomplished since the days of the Roman Empire (although Charlemagne had nearly done so around 800 CE).
In most European countries, subjugation in the French Empire bought with it many products of the French Revolution including democracy, due process in courts, abolition of privileges, etc. The increasing prosperity of the middle classes with rising commerce and industry meant that restored European monarchs found it difficult to restore pre-revolutionary absolutism, and had to retain many of the reforms enacted during Napoleon's rule. Institutional legacies remain to this day in the form of civil-law legal systems, with clearly redacted codes compiling their basic laws—an enduring legacy of the Napoleonic Code.
During the wake of the Napoleonic period, nationalism, a relatively new movement, became increasingly significant. This would shape much of the course future European history. Its growth spelled the beginning of some states and the end of others, as the map of Europe changed dramatically in the hundred years following the Napoleonic Era. Rule by fiefdoms and aristocracy was widely replaced by national ideologies based on shared origins and culture. Importantly, Bonaparte's reign over Europe sowed the seeds for the founding of the nation-states of Germany and Italy by starting the process of consolidating city-states, kingdoms and principalities.
The Napoleonic wars also played a key role in the independence of the American colonies from their European motherlands. The conflict significantly weakened the authority and military power of the Spanish Empire, especially after the Battle of Trafalgar, which seriously hampered the contact of Spain with its American possessions. Evidence of this are the many uprisings in Spanish America after the end of the war, which eventually led to the wars of independence. In Portuguese America, Brazil experienced greater autonomy as it now served as seat of the Portuguese Empire and ascended politically to the status of Kingdom. These events also contributed to the Portuguese Liberal Revolution in 1820 and the Independence of Brazil in 1822.
After the war, in order to prevent another such war, Europe was divided into states according to the balance of power theory. This meant that, in theory, no European state would become strong enough to dominate Europe in the future.
Another concept emerged – that of a unified Europe. After his defeat, Napoleon deplored the fact that his dream of a free and peaceful "European association" remained unaccomplished. Such a European association would share the same principles of government, system of measurement, currency and Civil Code. Some one-and-a-half centuries later, and after another major conflagration (the Second World War), several of these ideals re-emerged in the form of the European Union.