Final answer:
After the Kalinga War, Ashoka converted to Buddhism and actively promoted it throughout his empire.
Step-by-step explanation:
The religion embraced by Ashoka after the Kalinga War was Buddhism. Ashoka, the influential Indian ruler and a major figure in the spread of Buddhism, experienced profound remorse over the immense carnage of the Kalinga War, in which over 100,000 people were killed. This pivotal event led to his conversion to Buddhism, after which he implemented numerous reforms throughout his empire based on Buddhist principles, including non-violence, compassion, and general welfare. Ashoka also significantly contributed to the promotion and dissemination of Buddhism within India and across Asia, with his support for missionary efforts and monumental architecture.