philosopher, wrote "On the Law of War and Peace" in 1625, perhaps the first comprehensive analysis of international law. The philosopher Baruch Spinoza published substantial revisions of his mentor Rene Descartes' rationalist works, and also wrote a lengthy defense of freedom of conscience which was promptly denounced as heresy by his contemporaries. In art, an obscure portrait painter named Rembrandt van Rijn rose to prominence (and disapproval) for his religious paintings and figure studies. Peter Paul Rubens, a great painter in his own right, also ran an immense school for artists, attracting dozens of talented painters from all over Europe to the Netherlands. The mathematician Christiaan Huygens developed his wave theory of light, which was a giant leap in the study of optics pioneered by Isaac Newton. And biology was made incomparably easier by Antonie van Leeuwenhoek's invention of the microscope. After the Golden Age, the Netherlands retreated into the background, as the English fleet gradually achieved its supremacy. By the Napoleonic era, the Netherlands was once again dominated by its neighbors. In 1830, Belgium broke away from the United Provinces, in reaction to the restoration of the monarchy and the subordination of the Estates General, the council of stadtholders (provincial rulers). The Industrial Revolution came to the Netherlands as it did to the rest of continental Europe, and when World War I arrived, the Dutch remained neutral. The Dutch were not so fortunate during World War II, as Hitler's armies invaded and imposed their brutish rule. (The diary of Anne Frank, a Jewish girl living in Amsterdam, is considered a classic portrait of innocence confronted with great evil.) Despite an unusually active and vigorous resistance to the Nazis, which was often met with brutal reprisals, a great many Dutch Jews died in the Nazi death camps. After the war, the former Dutch colonies followed the pattern of other European colonies at the time, with independence and nationalist movements breaking out everywhere. Dutch politics were still characterized by religious divisions even until the 1970s, appropriately given the nation's history, but a more conventional parliamentary party system arose. Today the Netherlands, a thoroughly modern European nation, is best known for its hosting of international institutions such as the International Criminal Court in The Hague.