[Photo provided to China Daily]

Soldiers, military officers, students, civilians and overseas Chinese wrote to their families during China's War of Resistance against Japanese Aggression (1937-45).

Forty examples of this are included in Family Letters During War of Resistance against Japanese Aggression.

In the latest edition of the book, first published in 2007, another 15 letters are added to the original collection of 25.

Soldiers expressed their determination to fight to the death to protect the country and their compatriots.

Students asked their parents to forgive them for leaving home secretively in order to devote themselves to the cause of saving China.

Civilians escaped from occupied cities, drifting from place to place in homeless misery, telling their loved ones about life on the road.

Fathers never forgot to tell their children to be good people even during such horrendously difficult times.

Overseas Chinese sent their sons to the homeland to join the fight against the Japanese invasion.

"Family letters reflect that period from personal stories. It's a kind of reliable historical material," says Zhang Ding, director for the Research Center of Family Letters, Renmin University in Beijing.

He led the compilation for the latest edition of the book.

"We can see some military officials analyze in the letters the situations on battlefields and express their determination to fight," he says, adding that the psychology of civilians is also reflected in them.