World War I helped to push the Indian independence movement because the war brought hardship to India. In addition, the contributions made by Indians to the war effort caused them to expect better treatment by their colonial rulers.
It was after WWI that the movement turned to the sorts of tactics advocated by Mohandas K. Gandhi. The most dramatic change was the move to the non-cooperation strategy. This new strategy was the first to make the independence movement a broad-based movement. Before then, it had been an elite movement. Gandhi's tactics, by contrast, brought the masses into the movement. From then on, the movement was characterized largely by these sorts of mass tactics and non-violence.