 His belief was that churches should be self-governing, self-supporting, and self-propagating places of worship, free from government control. Thus, his churches became known as underground churches. Mingdao's evangelism came at a high price. When the Japanese occupied northern China in the late 1930s, the Chinese Christian Federation of North China bid to control the churches. Mingdao refused to join. He even kept a coffin in his house when he was threatened with execution.