It came together because colonial rule pressed on everyone in the same few ways, and because Indians slowly built the things a common struggle needs — shared grievances, shared organisations, shared symbols and shared methods. Diversity never disappeared; what changed was that local anger was converted into national action.
1. The grievances were common, even where the languages were not. Heavy land taxes produced famines and hit peasants and tribals from Punjab to Chota Nagpur. Cheap British manufactures ruined local industry. And the humiliation was identical everywhere: lower pay for Indians in the army, civil services and universities; juries with British majorities that were lenient towards Europeans; clubs, trains and city areas where Indians could not mix with Europeans; the Arms Act of 1878 that disarmed Indians but not the British; the Vernacular Press Act of the same year that censored Indian-language newspapers.
2. Organisations gave the anger an address. The Indian National Congress met for the first time in Bombay in 1885 with 72 delegates from diverse regions and religions, and after that it met every year in a different city. Regional bodies had failed; an all-India forum did not.
3. Newspapers carried one argument to many languages. Tilak’s Marathi Kesari, Bipin Chandra Pal’s and Aurobindo Ghose’s English Bande Mataram, the Bengali Yugantar, Naoroji’s Voice of India, Banerjee’s The Bengalee. A reader in Poona and a reader in Calcutta could be angry about the same thing on the same morning.
4. Symbols crossed language borders faster than arguments did. Bankim’s Bande Mataram, composed in 1875, became “a rallying cry and a mantra during the 1905 awakening”; Subramania Bharati translated it into Tamil; Lala Lajpat Rai named a Punjabi publication after it. Abanindranath Tagore painted ‘Bharat Mata’ in 1905. In Bengal in 1905 people tied rakhis on one another’s wrists to answer a partition meant to divide them.
5. The methods were ones anyone could join. You did not need English, a degree or a weapon to refuse foreign cloth, to spin khadi, to walk in a procession, to picket a liquor shop or to pick up a handful of salt. That is why the movement could include, in the words of a British report, “thousands of women, many being of good family and high educational attainments… actually from purdah”.
6. Shocks did the rest. The Partition of Bengal (1905), Jallianwala Bagh (1919), the all-British Simon Commission (1927), the lathi charge that killed Lala Lajpat Rai (1928), the executions of 1931 — each turned a regional protest into a national one.