The United States invade Iraq, assisted by the United Kingdom, Australia, and Poland. The Iraq War, which was termed illegal by then UN Secretary, Kofi Annan, caused hundreds of thousands of Iraqi deaths.
Japanese terrorists release poisonous gas in the Tokyo subway. 12 people died and thousands are wounded after members of the religious cult, Aum Shinrikyo, had places containers leaking sarin on 5 different trains.
Albert Einstein presents his general theory of relativity. The revolutionary theory describes the interdependency of matter on the one hand and space and time on the other. It is one of the most influential theories in Physics.