Assertion: There were instances of Kings belonging to castes other than Kshatriyas around the 6th century BCE and the following centuries.

Reason: Political power was effectively open to anyone who could muster support and resources, and rarely depended on birth as a Kshatriya.

Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Several important ruling lineages probably had different origins. The social background of the Mauryas, who ruled over a large empire, has been hotly debated. While later Buddhist texts suggested they were Kshatriyas,
Brahmanical texts described them as being of “low” origin. The Shungas and Kanvas, the immediate successors of the Mauryas, were Brahmanas. In fact, political power was effectively open to anyone who could muster support and resources, and rarely depended on birth as a Kshatriya.