What caused the collapse of ancient Egypt, ancient India and ancient Babylon?

Egypt was invaded by Romans, and now it is invaded by Arabs.

Ancient India was invaded by Aryans and msl successively.

Ancient Babylon was invaded by Elamites, Hittites and Assyrians.

The above three civilizations have obvious characteristics, invasion. This is not only military, but also demographic. When the aborigines only occupy a small part of an area, it is not far from extinction. Copts, like the direct descendants of ancient Egyptians, only account for 15%~20% of Egypt's total population. One day, if we are less than 50%, we are not far from extinction.

As for the last question, it's sheer nonsense. There was a hierarchical system in the Yuan Dynasty, and there were few marriages between different levels. As for those views, they all came from a history book compiled by a Manchu in the late Qing Dynasty (I forgot), and some of them were pieced together. What's the first night's right is also copied from some unofficial history of European medieval aristocrats, which is not credible. What kind of good words can you expect from a Manchu? )

In fact, there are many things in history that can't be married, such as Xianbei people and Han people don't get married, and Banners and Han people don't get married. As for those messy views, they all come from street literature, and there is no mention in the history books that the Han nationality is purer than you think.