You don't need a revolutionary ideology to hold together different languages and ethnicities. Just look at India.
I'm not sure if *India would have been possible pre-colonization though. At least not as a multi-ethnic state rather than as an Empire of one nation over the others. And I don't think a post-colonial union was what the OP had in mind...
I think it is a common misconception that India was never unified as a country before the establishment of the British Raj. True India was not politically unified as often as China. But several empires that came up in the subcontinent had brought large areas under their control for long periods. It may be noted that the area of the present Republic of India is 12 35 526 sq.miles(32 87 263 sq.kms).
The Maurya Empire founded around 320 B.C.E. covered an area of 19 30 511 sq.miles (50 00 000 sq.kms). The entire subcontinent except the southern and eastern tips were included in the Empire under Ashoka the Great. The Gupta Empire (13 51 358 sq.miles), the Pala Empire (17 76 070 sq.miles), the Chola Empire (13 89 968 sq.miles), the Mughal Empire (17 37 460 sq.miles) etc. covered larger areas than the present Republic. The Satavahana Empire, the Vijayayanagar Empire, the Maratha Empire etc, though were comparatively smaller also had brought large portions of the country under their rule.
Thus India was brought under one "chchatra"(umbrella) of an emperor several times in her long history.It was this common experience shared by the people of different religions, speaking different languages and following different customs and rituals that formed the foundation for the nation called 'India'.