Today marks the 71st anniversary of Japan’s surrender to Allied Forces toward the end of World War II. A research institution on Sino-Japanese history has released thousands of Japanese military mails during the war. The institution says the documents are new evidence that confirms the country’s invasion of China nearly 80 years ago.

“They are the first hand information that proves Japan’s invasion of China during World War II. It is not the memory of veterans. Instead, it recorded where and when the soldiers killed someone or occupied some place,” said Li Suzhen, executive VP of Japanese-Sino Society of Oral History Culture.

“I hope they are the last military mails of Japan. I wish our descendants never need to write this kind of mail again. We must reserve these letters and make public know about these facts,” said a member of the council of the Japanese-Sino Society of Oral History Culture.

The institution has collected more than 2,000 military letters from civilians across Japan. The letters  were written between 1937 and 1945 by Japanese military forces across China. The society confirms the authenticity of those mails and plans to translate and publish their contents in books in both China and Japan.