SEOUL, South Korea — South Korea’s Supreme Court on Thursday acquitted a man who refused to serve in the military because of his religious beliefs, a ruling expected to affect the fate of the more than 900 conscientious objectors who are currently on trial for refusing mandatory service in the country’s armed forces.

For decades, South Korea has required all able-bodied men in South Korea to serve in the armed forces and granted few exemptions under a conscription system seen as crucial to the country’s defense against North Korea.

It has billed military service as a patriotic duty, and the punishment of those who refused to serve has been both uniform and harsh. Each year, South Korea has sent hundreds of young men, most of them Jehovah’s Witnesses, to prison by invoking its Military Service Act, which calls for up to three years in prison for those who refuse to serve without “justifiable” reasons.