Building begins

Before the memorial hall opened, Cao often took his collection to show troops and schoolchildren in the city, garnering a strong reaction.

"Their response gave me great support to continue," he said. "To make it become a permanent exhibition, I submitted an application to the local government for land to build on in 2000."

The government quickly approved his application in accordance with the national public land policy.

But Cao encountered many difficulties, chief of which was raising money to pay for construction work.

"Because of being busy with collecting, I had stopped my business of growing and selling vegetables around 2000. I had spent almost all my savings on collecting. Fortunately, my wife gave me great support. She did various odd jobs to support the family and my dream," he said.

With the money he borrowed from relatives and friends, Cao started construction of the hall in September 2001.

On the opening day, he hung a banner proclaiming "Let the children know the history" on the wall. "It is a promise to the children as well as to myself," he said. "No matter what difficulties I meet, I will stick to it."

Cao has donated nearly 300 documents and relics valued at about 100,000 yuan ($14,000) to several museums in the country. They include the Museum of the War of Chinese People's Resistance Against Japanese Aggression in Beijing, the Memorial Hall of the Victims in the Nanjing Massacre by Japanese Invaders and the Museum of Evidence of War Crimes by Japanese Army Unit 731 in Harbin.

In April 2016, Cao founded a volunteer team named Peace, which has attracted more than 300 members from around China.

The volunteers protect history and culture related to the war, promote national spirit and patriotism, and advocate peaceful development.

"I have become used to my busy but impoverished life. But when I see more people can enjoy the happiness brought from our strong motherland, I think it's all worth it," Cao said.