Because principles is to examine the causes of difference. All these countries have gravity, and air, and wind, and weather.

One good example is Latin America. What we today call modern medicine actually came from Latin America. This is because the climate had a lot of heat and humidity, which is perfect for biodiversity. Barks, roots, fruits, seeds, animal products, and so on.

All manner of chemicals and ingestible things whose active ingredients could be extracted and concentrated and diluted and combined with reagents to produce medicine.

Now of course we make a lot of it synthetically in factories, but these natural conditions really boosted medical research. That's why a lot of Latin American countries have so many medical institutions.

People were shaped by their environment, which became culture, traditions and customs. For instance Islam and Christianity both come from scarce environments, relying on a lot of trade and expansion, so they move all over the world.

Compare this to Hinduism, which exists in a very lush and rich landscape in India, with lots of food sources and farmable land and high demand for labour. Suddenly we see dense and highly populated societies, and very little diffusion of religious faith outside of immediate regions.

You can find any number of principles which connect people who might seem unfamiliar or foreign to one another when you look at their environment.