The Yamnaya civilization emerged five thousand years ago (around 3300 BC) in the region between the Southern Bug, Dniester, and Ural rivers (the Pontic steppes). In his book Who We Are and How We Got Here, David Reich says that the Maikop culture or the people who preceded them made a genetic contribution to the Yamnaya population. Maikop technology of horse-drawn wheeled carts, and their way of raising mounds of earth and stone over graves, which are known as Krugans, was passed on to the Yamnaya.
The Yamnaya spoke a late Proto-Indo-European language. About 46 percent of the world’s population (3.2 billion people) speaks an Indo-European language as their first language. They could be biologically related to the Yamnaya. There are striking parallels between the Yamnaya and Europe’s Corded Ware culture—both could have descended from genetically similar pre-Yamnaya populations. The presence of Corded Ware culture is seen as evidence of the Westward expansion of the Yamnaya.
In his book The Horse, the Wheel, and Language, David W. Anthony says that Yamnaya were more efficient in managing their resources than their predecessors, the Maikop culture and others, and they replaced the population of any area that they came to dominate. Genetic studies show that the Yamnaya started dominating Europe in 3000 BC, and their descendants reached South Asia in a thousand years (between 2000 to 1800 BC). They transformed the demography of Europe and several parts of Asia.
Britain is separated from the rest of Europe by the English Channel, but the Yamnaya found a way of moving into the British Isles. 90% of the people who built the Stonehenge no longer exist. They were replaced by people who have Yamnaya ancestry.
Genetic studies show that the present day population in North India has a strong connection with the Yamnaya. The period between 2000 and 1800 BC, when the Yamnaya are believed to have arrived in North India coincides with the fall of the Harappa Civilization. It would be simplistic to hold the Yamnaya responsible for the fall of the Harappa Civilization. The Harappans were not a warlike people. Historian Gordon Childe found the Harappa civilization to be unique in its lack of attention to weapons of war.
The ruins of Harappan towns and cities show no sign of external attack. Most buildings are well-preserved and seem to have been abandoned. People probably migrated to other parts of India. Disease, environmental factors, and sudden decline in trade (due to the fall of the Mesopotamian civilization) might have something to do with the fall of the Harappa civilization.
Many historians believe that the branch of Yamnaya civilization which arrived in North India spoke Vedic Sanskrit and they could be the primary creators of several ancient Hindu texts (particularly the early texts). After 1800 BC, Vedic Sanskrit started taking root in North India. Some scholars have posited that the present day Tamil language has some similarities to the Harappa script. If this is true, then it might be surmised that as the Yamnaya spread their dominance in North India, the Harappans migrated to the South.
The Harappans were acquainted with horses and chariots but the Yamnaya could have played a major role in popularizing the use of horse-drawn wheeled chariots for transportation and warfare. The Harappa script has not been deciphered, and there is a lot of controversy about Harappan religion and politics. We don’t know if there is any connection between Yamnaya and Harappan religious and political thinking. The word “Yamnaya” means related to pits (or graves) in Russian, but in Sanskrit, it points towards “Yama,” the Hindu god of Death and Justice.
The Harappa civilization extends back to 3300 BC, which is the same period when the Yamnaya civilization came up in the Pontic steppes. Perhaps there was a connection between the Harappans and the Yamnaya from the early days of both civilizations. But I have not found this being suggested in the work of any historian.