The 20th (twentieth) century began on January 1, 1901 (MCMI), and ended on December 31, 2000 (MM). The 20th century was dominated by significant events that defined the modern era: Spanish flu pandemic, World War I and World War II, nuclear weapons, nuclear power and space exploration, nationalism and decolonization, technological advances, and the Cold War and post-Cold War conflicts. These reshaped the political and social structure of the globe.