What is the reason for the decline of Indian Valley civilization?

Indian valley civilization declined in the first half of the second millennium BC, and seemed to end around 1600 BC. The reason is still under debate. An important disturbing factor may be a series of floods and earthquakes, which diverted the Indus River and flooded densely populated areas. At the same time, northwest India was invaded by semi-civilized tribes, and those warriors destroyed the city and occupied the land. However, people no longer believe that the Indian valley civilization suddenly collapsed, or that the barbarian invasion led to the decline. The invaders brought the seeds of India's new civilization, but they also merged with the conquered residents, absorbing and continuing many factors of indigenous culture.

The coincidence of the invasion and the decline of early Indian civilization is not an isolated event in the world. In the late 2000 BC, some environmental factors-perhaps the continuous decrease of grasslands in Central Asia and West Asia-including the large-scale migration of nomadic people also appeared. Immigrants mainly settled in the south and west of Asia (for example, the Hittites occupied Anatolia in about 1 600 BC), but the cultural effect produced by this population movement is far more profound than the regional material effect. Although the immigrant tribal society is primitive and lacks writing system, their spoken language is very developed and tends to replace the spoken language of the residents. The modern term "Indo-European language family" refers to an overwhelming language family from Hindustan to the western and northern borders of Europe. It includes ancient Greek and Latin, as well as modern European languages-Greek, Romance, Slavic, Cartesian and Germanic (the main exceptions are Hungarian, Finnish and Estonian).

During the great migration in the first half of 2000 BC, two closely related tribes migrated from the grasslands in western Russia to the southeast, one entered the Iranian plateau, and the other crossed the Hindu Kush mountains into the northwest of India. These two types of people call themselves "Aryans" (meaning "nobles"); The geographical and political term "Iran" came from this, and some Indian variants of this word also came from this. Strictly speaking, the name Aryan is only applicable to Iranians (Persians) and Aryans in India in the subcontinent, although it is often widely used throughout the Indo-European language family. It is inappropriate to call any European country or race by it.