The Allies occupied Japan until 1952, during which a new constitution was enacted in 1947 that transformed Japan into a constitutional monarchy. After 1955, Japan enjoyed very high economic growth under the governance of the Liberal Democratic Party, and became a world economic powerhouse. Since the Lost Decade of the 1990s, economic growth has slowed. On March 11, 2011, Japan suffered from a magnitude 9.0 earthquake and tsunami, one of the most powerful earthquakes ever recorded, which killed almost 20,000 people and caused the serious Fukushima Daiichi nuclear disaster.