Austria has a population roughly the same size as that of Greater London (8.7 million). It was born from the Holy Roman Empire, under the Habsburg dynasty. The Emperor's power remained strong in the south as the northern German princes started to resent being controlled, using Protestantism as the flag of rebellion. The Austrian Empire was proclaimed in 1804 in response to Napoleon's self-coronation as Emperor of the French, becoming part of the Austro-Hungarian Empire in 1867. The fragile balance of power maintaining peace since the Thirty Year War saw various empires forming frenemies. Ferdinand II started that war (1616-1648) trying to impose religious uniformity in the form of Roman Catholicism. Austria was the first to go to war in 1914, becoming WWI, following the assassination of its Archduke, Franz Ferdinand.