Napoleon rose to power in France through his military successes and ambition. He introduced important reforms including the Napoleonic Code and established a public school system. By 1812, Napoleon had come to dominate most of Europe by rapidly moving large armies and annexing some lands while forcing alliances on others. However, nationalism in European states, guerilla warfare in Spain, and the devastating winter in Russia threatened Napoleon's empire and ultimately led to its downfall. Napoleon left a lasting impact on Europe and the world by spreading nationalism, facilitating American expansion, and abolishing the Holy Roman Empire.