Various factors were responsible for the spread of the leftist trend in the national politics.
(1) Success of the Bolshevik Party in Russia created a new hope amongst some people in India. If the common people of Russia could overthrow the mighty Tsarist regime the Indian people could also drive the English out of the country.
(2) Socialist ideas began to spread among some people who participated in the Non Co-operation Movement. For, they were unhappy with the outcome of Gandhian policies.
(3) Several socialist and communist groups came into existence all over the country.
For example, S.A.Dange in Bombay, Muzaffar Ahmed in Bengal and others started propagating leftist ideas through the journals published by them. These were the reasons why there was the spread of the leftist trend in the national movement.