Primarily it was Nehru and Jinnah. Rest of the pieces fell in their place. Both were exposed to the western world and both were ambitious. Both wanted the best for themselves. Rest is just the justification. Jinnah died earlier without reaping the power. Nehru lived longer to enjoy the power and passed it along his family. Rest as they say, is history.
Funny thing is that Iqbal, often credited for concept of Pakistan never wanted a separate country but a state in which Muslim can live according to their traditions.
United India never had a lingual/religious/skin-color based identity and would have dragger herself with few hitches here and there.
One school of historians has it that the communal element in modern India, as distinct from mediaeval India, was re-ignited by the British, perhaps inadvertently, due to their sheer ignorance of Indian society, and their concurrent need to find out how to administer this society.
Whether it was William Carey at the Fort William College, charging into vernacular languages with the help of Brahmin scholars learned in Sanskrit, or William Wilson Hunter, writing his definitive but tragically flawed "
The Indian Musalmans: Are They Bound In Conscience To Rebel Against The Queen?", or H. H. Risley, writing the monumental "
The Tribes and Castes of Bengal", one reads their work with divided feelings: one is in the presence of a Titan, and simultaneously, one realises with a thrill of horror the injection into Indian society of the viral strains that cause most of the diseases of society today.
There is nothing that I know of William Carey's work that is readable today, other than for very narrow-band research, but his dependence on Brahmins for defining, codifying and conducting etymological studies into, for instance, Bengali created a massive split within the community. It has been argued that the increasing influence of Arabic and right-to-left scripts on Bengali as it originally was, or the neglect of the 'puthi', or the complete dependence on the Nadia dialect for a template for standard Bengali disenfranchised the bulk of the Bengali-speaking people, a condition that is being reversed in Bangladesh, but naturally does not fill a West Bengali's heart with much joy. This by itself is a complex subject and would with minimal effort yield an MPhil at the least; with some serious effort, a PhD or ten.
I read Hunter when I was naive (even more than I am today) only conscious of standing in the presence of a significant trans-cultural personality. Reading him after 30 years, the damage that he did, and that other British administrator-scholars did to Indian society is starkly visible. If you like, this was the genesis of Pakistan. If you can get your hands on it, read the book. It is scary, but instructive.
Risley's book was the love of my life in my teens. We had two of his four volumes at home, and it was SUCH FUN to memorise the matching algorithms for Kayasthas to be paired for marriage; it took specialists and covered eight or ten pages in his book, perhaps more; I forget. It defined who could marry whom, down to the seventh son and seventh daughter, and including Kulin Kayasthas, those of superior descent compared to others, normally a category linked to Brahmins, and also a category that led to hundreds of child brides being murdered by enforced suttee.
At the time, it was fun. But reading about his methods of race-classification through physical anthropometry brought the awful realisation that this was a racist of a high degree of sophistication. I hate to mention this, but his wife, an 'erudite German', is an obvious suspect. Nobody may have maimed Indian social analysis as gravely as Risley. His classification of Indians into 'races', his use of the nasal index to determine 'race', his absurd sample sizes, useful only to the extent that they yielded data to support his theoretical architecture, his interpretations of the Census, that made them the subjects of avid study by scholars throughout the world - there is a succession of grenades with the pins taken out in his work.
By the time that Jinnah and Nehru and our own muddle-headed Mahatma came on the scene, the bulk of the intellectual damage had been done. British colonial thinking, therefore responses to this thinking, therefore the nationalist movement, in some respects formed as a pure anti-thesis to the theses of the British and their thinking, were all implacably in place, and are being pried loose only in the last few decades.
You might look at your post once again, and track how what you said reflects a reality so heavily influenced by these almost unknown scholars and administrators. I am referring to an ideological reality.