One of my pet peeves is that it is ridiculous to compare nation-states when they are not comparable. For example, China and Switzerland are both nation-states. But China has a continent scale population, but, less ethnic diversity than Switzerland.* Similarly, you can’t compare some European nations to the United States. Rather, the better point of comparison is to some American states.
A similar problem crops up when you compare India to Pakistan. Though Pakistan has some within nation diversity, India is arguably much more diverse. And some of the “states” within India are enormous in size and population. The North Indian state of Uttar Pradesh actually has a larger population than Pakistan by 20 million! But there’s another aspect of the variation that I’ve always found of note: the social statistics of BIMARU, the core North Indian Hindi-speaking states, resemble Pakistan more than they resemble other Indian states.
Below I’ve plotted the total fertility rate at three time points for various states and nations. What is striking is that not only do Bihar and Uttar Pradesh resemble Pakistan in total fertility rate, but they follow the same trajectory. In contrast the state of Punjab, which is ethnically similar to Pakistan, and sits geographically between BIMARU and Pakistan, has sub-replacement fertility, like Tamil Nadu in the deep south of India.
* China has more minorities, but there is far less balance. It is 90-95 percent Han Chinese.