Final answer:
The Kushan Empire arose in NW India after the fall of the Mauryan empire and played a key role in trade and cultural exchange along the Eurasian trade routes.
Step-by-step explanation:
The regional kingdom that arose in NW India after the collapse of the Mauryan empire and served as a key link to Eurasian trade routes was the Kushan Empire. The Kushans, who established themselves in northern India and parts of Central Asia, played a crucial role in stabilizing the trading routes connecting India with China and the Mediterranean. They facilitated trade and cultural exchange between these regions, contributing to the spread of Buddhism and Greek influences in India.