Why did Che Guevara join Fidel Castro’s 26th of July Movement?

Che Guevara joined the 26th of July Movement after meeting Fidel and Raúl Castro in Mexico. The Castro brothers were political exiles actively organizing a guerrilla force to overthrow the dictatorship of Fulgencio Batista in Cuba.1

Guevara initially joined the movement to serve as the force's doctor, though he had also received training in the use of weapons. He subsequently became one of Fidel Castro’s most trusted aides and a key figure in the guerrilla army that operated from the Sierra Maestra mountains.1