Duan would carefully search and verify each item before he decide to acquire it, and years of study and extensive reading have made Duan an expert himself. He can easily tell the differences between different types of weapons and uniforms, among other things, accurately identifying the factories and the year in which they were produced.

In the eyes of Duan's friend Ge Shuya, a local expert on the War of Resistance in Western Yunnan, Duan's limited income in the early years forms a sharp contrast with his rich collection now.

"He had to live a frugal life back then, but he didn't balk at paying for relics he believed were important," Ge says.

Spending almost all of his salary on his collection, Duan had to apply for loans in order to support his family. Later, Duan started collecting more valuable antique pieces that he could sell to repay his loans.

Duan estimates that, over the course of his 30-years of collecting, he has spent more than 30 million yuan ($4.4 million) collecting relics and items related to the War of Resistance in Western Yunnan.

Despite the misunderstanding and doubts of others, even being called "crazy" by people - including members of his own family - Duan says that he doesn't regret devoting himself to his collection.

"It's about Tengchong's history, it's very important," says Duan.