For descendants of the millions in Asia who were killed or brutalized in a war started by Imperial Japan, Mr. Gerteis said, the ruling is a stark reminder. “This was their holocaust,” he said.

Here is some background on the South Korean court’s ruling and what it could mean going forward:

What did the South Korean court decide?

It upheld a lower-court ruling in 2013 that Nippon Steel & Sumitomo Metal must pay 100 million won, or about $88,700, to each of four South Korean men who said they had been subjected to forced labor between 1941 and 1943. Korea was a Japanese colony from 1910 until Japan’s surrender in 1945. The ruling could apply to pending cases involving other companies accused of using forced labor.

The court said there was nothing in postwar agreements or international law that prevented individual victims from seeking redress.

The Nippon Steel case has added resonance because the lawsuit was filed more than 20 years ago, and nearly all former forced laborers there who could have received compensation have since died. “I am the only one still alive to see this day come,” Lee Chun-shik, 94, the surviving plaintiff, told reporters outside the courthouse.

What are the broader implications?

The verdict could open the floodgates for other victims and their relatives to file lawsuits against an estimated 300 Japanese companies accused of using forced labor during the colonial era.