For more than a century, India and Pakistan were ruled as one country – including Bangladesh and, sometimes, Burma and Sri Lanka, too. Both main parts of the old British Raj have similar ethnic hodge-podges, internal language barriers, basic unfamiliarity with democracy, etc.
Both India and Pakistan suffered tremendous human and political losses as the British pulled out all-too-quickly in 1947. In fact, all that really separates them is religion — India with Hindu and Pakistan with Islam. But neither religion was ever much geared to the modern democratic experience. Look at India today, modernizing and free-ish, and look at Pakistan, back under martial law. Again.
So why did democracy take root in India but not in Pakistan? What went wrong?