Josef Stalin's rival Leon Trotsky was assassinated August 21, 1940, in which country?

After losing a bitter power struggle with Joseph Stalin for control of the Soviet Union, Leon Trotsky was forced into exile in 1929. For years, he was a political outcast, moving between Turkey, France, and Norway, with few countries willing to grant him refuge for fear of angering the powerful Soviet leader. In 1936, a safe haven was finally offered by the left-leaning government of Mexican President Lázaro Cárdenas. Trotsky and his wife settled in a suburb of Mexico City, initially staying with the famous artists Diego Rivera and Frida Kahlo.

Even thousands of miles from Moscow, Trotsky was not safe from Stalin’s reach. He lived in a heavily fortified compound in Coyoacán, which survived a machine-gun assault by Stalinist agents in May 1940. The final, fatal attack came from within. An NKVD agent named Ramón Mercader, posing as a sympathetic follower, spent months gaining Trotsky’s trust. On August 20, 1940, Mercader was granted a private meeting in Trotsky's study, where he struck the revolutionary leader in the head with an ice axe. Trotsky died from his wounds (Review) the following day, ending one of the 20th century's most significant political rivalries.