"Three years" refers to the period of the Liberation War (1946—1949);

Thirty years "refers to the period of the new-democratic revolution from the May 4th Movement (1919-1949), which marks the beginning of the new-democratic revolution;

"Dating back to 1840" refers to the whole period of democratic revolution from the Opium War (1840- 1949).

"1840" was the beginning of China's invasion. 1840 After the Opium War, China became a semi-colonial and semi-feudal country, marking the beginning of modern history of China.

Extended data:

Inscription on the Monument to the People's Heroes:

On the front, Mao Zedong inscribed eight gold-plated characters with the inscription "People's heroes are immortal"; On the back is an inscription drafted by Mao Zedong and inscribed by Zhou Enlai:

In the past three years, the people's heroes who died in the People's Liberation War and the People's Revolution are immortal!

For more than 30 years, the people's heroes who died in the people's liberation war and the people's revolution are immortal!

This can be traced back to 1840. Since then, in order to oppose domestic and foreign enemies, strive for national independence and people's freedom and happiness, the people's heroes who died in previous struggles are immortal!

Baidu Encyclopedia-Monument to the People's Heroes Inscription