Daniel Manning 
Mobilization certificate photo of Park Dongfu (Japanese name: Yamamoto Towa). Said to be taken at the time he was mobilized to the Kawasaki Steelworks in Iwate Prefecture. No year of photography is recorded. He is smiling in front of a massive machine. (Courtesy of Ryosuke Nagatani)
The wartime labor issue concerning Korean workers mobilized to Japan during World War II is contentious among scholars and in Japan-South Korea relations. It was one of the issues settled under the 1965 Treaty on Basic Relations. Japan provided $500 million (roughly equal to $5 billion today) in aid and loans to South Korea, with both countries agreeing that all claims, including those of wartime laborers, were fully and finally resolved. However, certain Japanese scholars and many in South Korea still maintain that Japan subjected Koreans to forced labor.
One of the key figures challenging this narrative is historian Ryosuke Nagatani, PhD. Nagatani has critically examined primary sources related to the Nisso Tetshio Coal Mines and the Sado Gold mines to reassess long-held claims on the Korean side. He argues that much of the forced labor narrative is built on testimonies that came decades after the fact rather than contemporary records and concrete documentary evidence.
Through meticulous analysis of payroll records, company correspondence, and official government documents, he challenges popular Korean historical perspectives. In an exclusive interview with JAPAN Forward, he discusses his key findings and the broader implications for Japan-South Korea relations. Excerpts follow.
No year of photography is recorded. The photo was taken a year after he first started working in a Japanese coal mine. His robust physique after one year of labor is evident. (Courtesy of Ryosuke Nagatani)
The Wage Exploitation Question
Your research is based on primary sources. What key documents did you find, and how do they differ from the forced labor narrative?
Nisso Teshio Coal Mines had the largest number of primary source documents available, and many of them clearly contradict the popular narrative.
One of the most representative arguments by those who advocate the "forced labor" argument is that Korean workers had their wages exploited. That is, they earned money but had most of it taken by the companies, leaving them with almost nothing in the end. However, actual payroll records remain from that period. By examining them, it is clear that Korean workers were receiving substantial wages.
Among these workers, some sent money home to their families, while others did not. They had the freedom to do as they pleased with their earnings.
At the time, this was similar to what applied to Japanese workers as well. There was a wartime savings system called aikoku chokin (patriotic savings), where a portion of workers' wages was deducted as a mandatory government tax. However, the deduction for Korean workers was only 10-20% of their wages, which is too small an amount to be considered "exploitation."
Furthermore, there were cases where some Korean workers who earned less due to working fewer hours were exempt from aikoku chokin deductions altogether. This was a new discovery in my research — something that no one had pointed out before. It provides a more accurate picture of the actual working conditions of Korean laborers at that time.
Said to have been taken while working at the Kumada Coal Mine of the Iizuka Mining Office in Fukuoka Prefecture. Their muscular physiques are visible. No year of photography is recorded. (courtesy of Ryosuke Nagatani)
Willing Workers
Another surprising finding was that some Korean workers wrote letters of appreciation to Nisso Teshio after returning to Korea.
For example, one worker's wife became seriously ill, and he requested permission to return to Korea to care for her. The company granted him permission to leave. After he returned home, he sent a letter to Nisso Teshio, expressing his gratitude.
In the letter, he wrote:
"I was able to return home to care for my wife thanks to your kindness. I am truly grateful. Once my wife recovers, I would love to return to work at your company, but unfortunately, her condition has not improved. Still, I will never forget the generosity your company has shown me."
This makes one wonder — is this the kind of letter a so-called "slave laborer" would write?
An interesting 1974 letter written by a former employee of the Sado Mining Company has also been preserved. In this letter, the employee describes visiting Korean villages to recruit workers.
According to the letter, the company aimed to recruit 20 workers from a particular village. However, when they arrived, 40 people showed up, eager to work, which created difficulties in selecting candidates.
The letter clearly states that many people actively sought these jobs. If we follow the logic of forced labor proponents, this situation does not align with their claims of coerced labor.
Some claim that Korean workers at the Sado Gold Mines were forced to stay even after their contracts ended. What do historical records show?
There is a tobacco rationing ledger from the Sado Gold Mines that has survived, and it contains lists of Korean workers who completed their contracts and returned home.
From my research, I found six different pages of these records, all from 1945, the year the war ended. These pages list around 30 workers who returned to Korea.
In other words, there is clear documentation that workers completed their contracts and returned home, contradicting the claim that they were forcibly held against their will.
The Challenge of Oral History
How do oral testimonies compare to primary source documents?
One of the biggest challenges with testimonies is inconsistency. For example, let's take the issue of wages. Some workers (at Hashima) testified that they received their wages. Others who worked at the same site during the same period claimed they never received any wages at all.
We see the same pattern in Sado Gold Mine testimonies. Certain workers said they were paid and were able to spend their money freely outside the work site. Yet others claimed they were confined and could not spend their money, so they saved it instead. With such contradictory testimonies, it is extremely difficult to determine what actually happened.
In my research in 2022, I reviewed testimonies from 147 people related to the Sado Gold Mines. The South Korean government collected these war-era testimonies about the Sado Mines in 2005. Trying to reconcile their inconsistencies was a significant challenge.
This is why testimonies alone are unreliable. They must be cross-referenced with primary source documents to determine whether they are historically accurate. Currently, various foundations and research groups in Japan and South Korea are collecting testimonies. Although they have managed to gather nearly 150 testimonies, they are not conducting verification work.
This is what I find frustrating. If they have already gone through the effort of gathering these testimonies, why not move forward with verification?
Have you noticed changes in the historical perception of the issue?
Yes, I believe perceptions are shifting. A major factor is the Sado Gold Mine's World Heritage nomination, which led to a new museum in Aikawa City featuring an exhibit on Korean laborers.
Despite South Korean lobbying, the exhibit does not state that Koreans were forcibly mobilized or subjected to forced labor.
What message do you want to convey through your research?
My research directly challenges the popular Korean narrative. The idea that Koreans were forcibly mobilized by Japan has been treated as an unquestionable historical fact for decades in South Korea. Anyone who dared to question it faced persecution within academic circles. However, historical inquiry must be based on primary sources and rigorous analysis.
Through my work, I highlight how key evidence contradicting the forced labor narrative has been ignored or deliberately excluded. For example, records show that Korean workers completed their contracts and returned home, yet these documents are often left out of discussions.
Similarly, recruitment records demonstrate that Koreans actively sought these jobs, contradicting claims of abduction or coercion.
It is estimated that this photo was taken in June 1944 when he was mobilized to Unit 13052, Fourth Company. He is shown smiling with his arm linked with a colleague. (Courtesy of Ryosuke Nagatani)
If history is to be a serious academic discipline, scholars must ask difficult questions. For example, why do testimonies change over time? Why are contradictory statements ignored? And why are primary sources dismissed when they do not align with dominant narratives? These are the questions that should guide our understanding of the past.
I believe that history should be examined through evidence, not emotional rhetoric or political motivations. The goal of my research is not to diminish Korean suffering but to establish a more accurate historical account based on facts. Only by confronting historical distortions can Japan and South Korea move forward toward genuine reconciliation.
RELATED:
- Sado Gold Mines and Seeking a Balanced Historical Perspective
- Former Hashima Residents Challenge NHK's Falsified Video of Wartime Labor
- EDITORIAL | Bad Faith in Sado Mines Rites Boycott by Seoul
Author: Daniel Manning
