Trotsky was exiled from the Soviet Union in 1929, once Joseph Stalin had consolidated his power. From that time on, Trotsky moved to different places around the world. In 1936, Trotsky settled in Mexico, where he stayed until he was murdered in 1940.
Trotsky's death in Mexico was the result of Stalin perceiving him as an enemy. Once Vladimir Lenin died, a power struggle developed between Trotsky and Stalin. Things between both men were so divisive that Stalin lied to Trotsky, who was traveling out of the country when Lenin died, about the date of the funeral. Stalin did this so he could be seen as the inheritor of power without Trotsky there. Trotsky was perceived as the greater revolutionary. He was seen as the theoretician seeking to keep the Russian revolutionary spirit alive. Stalin was more pragmatic about having power and controlling all activities under one Russian state of which he was the unquestioned head.
After Lenin's death, Trotsky sought to embrace a nuanced political approach that would allow him to be seen as the next in line to take over. He made speeches, talked about the struggle of Bolshevism, Communist rule, and developed theoretical positions that justified his claims. Stalin simply sought to consolidate power using secret police, propaganda, and political pressure to ensure that no one would speak out against him.
Over time, Stalin was able to manipulate the situation so that his power increased and Trotsky was marginalized. Stalin was able to pass provisions into law that made it a punishable offense to hold an opinion that was contrary to party leadership. Having to confront a political reality of which he was no longer a viable part, Stalin expelled Trotsky from Communist Party activities and then exiled him out of the country.
Once exiled from Russia, Trotsky traveled around the world for sanctuary. He spent time in Turkey, France, and then in Mexico. While in Mexico, Trotsky wrote extensively on the Russian Revolution and how Stalin's rule twisted the revolutionary spirit. His writing sought to suggest that he would have served the goals of the revolution had he been in a position of power, and that Stalin worked to increase his own power and not for the revolutionary cause.
Ever paranoid and determined to eliminate all enemies near or far, Stalin used his secret police to kill Trotsky. On November 20, 1940, while Trotsky was reading in his study in Mexico, he was bludgeoned in the head with a pickaxe. The blow to the head did not immediately kill him, but upon being rushed to the hospital, he died the next day of blood loss and head trauma.