The fall of the Mauryas left the Khyber Pass unguarded, and a wave of foreign invasion followed. The Greco - Bactrian king, Demetrius, capitalized on the break - up, and he conquered southern Afghanistan and parts of northwestern India around 180 BCE, forming the Indo - Greek Kingdom. The Indo - Greeks would maintain holdings on the trans - Indus region, and make forays into central India, for about a century. Under them, Buddhism flourished, and one of their kings, Menander, became a famous figure of Buddhism; he was to establish a new capital of Sagala, the modern city of Sialkot. However, the extent of their domains and the lengths of their rule are subject to much debate. Numismatic evidence indicates that they retained holdings in the subcontinent right up to the birth of Christ. Although the extent of their successes against indigenous powers such as the Shungas, Satavahanas, and Kalingas are unclear, what is clear is that Scythian tribes, renamed Indo - Scythians, brought about the demise of the Indo - Greeks from around 70 BCE and retained lands in the trans - Indus, the region of Mathura, and Gujarat.
who invaded south asia and set up a state following the mauryan period
The Greco - Bactrian king, Demetrius