Influenced by the new ideas of the Enlightenment, the American Revolution (1765–1783) is usually considered the starting point of the Age of Revolution. It in turn inspired the French Revolution of 1789, which rapidly spread to the rest of Europe through its wars. In 1799, Napoleon took power in France and continued the French Revolutionary Wars by conquering most of continental Europe. Although Napoleon imposed on his conquests several modern concepts such as equality before the law, or a civil code, his rigorous military occupation triggered national rebellions, notably in Spain and Germany. After Napoleon's defeat, European great powers forged the Holy Alliance at the Congress of Vienna in 1814–15, in an attempt to prevent future revolutions, and also restored the previous monarchies. Nevertheless, Spain was considerably weakened by the Napoleonic Wars and could not control its American colonies, almost all of which proclaimed their independence between 1810 and 1820. Revolution then spread back to southern Europe in 1820, with uprisings in Portugal, Spain, Italy, and Greece. Continental Europe was shaken by two similar revolutionary waves in 1830 and 1848, also called the Spring of Nations. The democratic demands of the revolutionaries often merged with independence or national unification movements, such as in Italy, Germany, Poland, Hungary, etc. The violent repression of the Spring of Nations marked the end of the era.