Multiple choice The most important cause for the outbreak of the Gadar revolution was the arrest of Lala Hardayal outbreak of World War I hanging of Kartar Singh Sarabha Kamagata Maru incident Reveal answer Fill a bubble to check yourself D Correct answer Explanation The Kamagata Maru incident, where a ship carrying Indian immigrants was denied entry to Canada and subsequently faced a tragic confrontation upon returning to India, served as a major catalyst for the Gadar movement.