Chandragupta unified northern India in the 4th century BCE and defeated the Persian general Seleucus. He divided his empire into provinces and districts for administration and law enforcement. Chandragupta's advisor Kautilya wrote the Arthashastra, a guide for kings that supported strong central authority. In the 3rd century BCE, Emperor Asoka converted to Buddhism after a bloody battle and promoted Buddhist principles through edicts scattered across South Asia. The powerful Gupta Empire arose in the 4th century CE and saw economic prosperity through trade, as well as cultural and scientific achievements, but declined due to invasions starting in the 5th century CE, leaving India politically fragmented.