(a) Pressure Group is a term used for people or a group of people who work for a common cause. It is an organization where people actively participate and promote the cause, unlike political parties they do not participate in election proceedings.
(b) Congress started as a pressure group that represented the English speaking upper class, urban middle class, and elite class etc. But later as movements like Civil disobedience movement and Noncooperation movement launched, it attracted more rural people, students, workers, women towards itself.
The party started to represent all class people as a leader, this widened social base and by the time of independence, Congress transformed into a rainbow-like the social coalition.
(c) Congress started as a pressure group during the British regime and participated extensively in the freedom struggle of the nation. Gandhi Ji was also associated with the party, this led to the popularity of the Congress. The party professed unity, equality and propagated demands of each class of the society.
After Independence Congress party came into power and Jawaharlal Nehru became the first Prime Minister. Later when the coalition party system evolved and many state parties participated in the election, even then Congress led by Indira Gandhi emerged victories.
These led to the emergence of Congress as a mass political party.
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