How does the Pontic-Caspian steppe hypothesis explain the spread of Indo-European languages?

The Pontic-Caspian steppe hypothesis posits that the Proto-Indo-European language originated approximately 6,000 years ago in the region north of the Black Sea and Caspian Sea, encompassing parts of modern-day Ukraine, Russia, and Kazakhstan.1

This model suggests that speakers of the parent language were part of a homogeneous population associated with the Kurgan culture, a group of related steppe cultures. The spread of their languages is attributed to significant expansions and migrations that occurred during the fourth and third millennia BCE.21

Key factors facilitating this dispersal included:
* Technological Innovation: The region was transformed after 4000 BCE by the introduction of horse-drawn wheeled vehicles and other advancements.2
* Nomadic Efficiency: By 2000 BCE, these populations had developed a highly efficient nomadic way of life.3
* Military Advantage: Armed with battle-axes and supported by a superior food supply derived from animal husbandry, these groups moved into forested regions of Europe, overrunning existing farming and fishing populations and establishing their linguistic and cultural dominance.3

Subgroups subsequently diverged and spread across the Near East, India, and Europe.1