Mahatma Gandhi entered Indian politics through the Champaran Movement. This movement took place in 1917 in the Champaran district of Bihar. It was centered around the issues faced by the indigo farmers who were being forced to grow indigo by the British landlords. Gandhi, who had recently returned from South Africa, was invited by the farmers to help them fight against these oppressive practices.
During the Champaran Movement, Gandhi advocated for the rights of the farmers and organized protests and demonstrations. This marked the beginning of his involvement in Indian politics and his methods of nonviolent resistance. The success of the Champaran Movement propelled Gandhi into the national spotlight and paved the way for his future leadership in the struggle for Indian independence.
In conclusion, the correct option is 2 - Champaran Movement.