Step 1: Gandhiji's Arrival in Champaran.
Gandhiji arrived in Champaran in 1917 after being approached by Rajkumar Shukla. The peasants were being exploited by the British planters who forced them to grow indigo, taking away a major portion of their crops.
Step 2: Gandhiji's Satyagraha Movement.
Upon his arrival, Gandhiji launched a non-violent movement (Satyagraha) to fight against the unfair treatment of the peasants. He organized protests, gathering public support, and demanded justice for the peasants.
Step 3: The Outcome.
The movement was successful in bringing the exploitation of the peasants to light. The British authorities were forced to grant the peasants relief, reducing the oppressive land tax and freeing them from the forced cultivation of indigo.
Step 4: Conclusion.
Gandhiji's efforts helped improve the conditions of the peasants, and the Champaran Satyagraha became a turning point in India's freedom struggle.
Final Answer: \[ \boxed{\text{Gandhiji launched the Champaran Satyagraha to end the exploitation of peasants by the British planters. His peaceful protests led to a reduction in the indigo tax and provided relief to the peasants, marking a significant victory in India's freedom struggle.}} \]