Buddhism was made the state religion of Silla (a kingdom in early Korea) because a court official planned his own martyrdom.
Making a religion the official state religion of a country is a difficult and controversial business. During the three kingdoms period of Korea – when the peninsula was divided into the independent realms Goguryeo, Baekje, and Silla – Buddhism was on the rise. Gorguryeo and Baekje had many prominent Buddhist converts, and they began to bleed into Silla as well. There’s a great folk tale about how Silla became a Buddhist country, one that involves the ultimate sacrifice.
The king of Silla, Beopheung, was sympathetic to making Buddhism the state religion. His royal court was enthusiastically opposed. One official was on his side, Beopheung’s “grand secretary” Ichadon. And Ichadon, a devout Buddhist, had a plan for how to convince the rest of the court: he insisted that the king kill him.
This being folklore, some of the details vary on how this deliberate martyrdom was planned. Either Ichadon used the king’s seal without his permission to make Buddhism the official religion, or he stood up in court and insisted that Buddhism be made the state religion. The king (secretly wise to the scheme) sentenced him to death. Ichadon replied that should he die in the name of Buddhism, his death would provoke a “divine event.”
Ichadon was decapitated in 527 CE. As his head came off, reportedly milk flowed out of his neck instead of blood, the skies darkened, and his head flew off into the mountains far away. A temple now stands on the supposed place where the head landed (it’s pictured above). The rest of the court was suitably awed by this miracle, and the king had no further trouble or opposition in his plan. Buddhism became the state religion of Silla the next year.