English breakup letter

It is a romantic thing for lovers to exchange love letters, but everyone is afraid that the above is: "We break up!" This must be heartbreaking. In the English "breakup letter", the captives have a common title - John.
“Dear John letter” originated from the Second World War. Since thousands of soldiers in the United States were stationed in foreign countries, their distance from their girlfriends or wives caused emotional barriers. When these gaps were communicated on the stationery, The time becomes: "Dear John, I have found someone else whom I think the world of. I think the only way out is for us to get a divorce."

Upon receiving such a letter, the soldiers were heartbroken one by one. Later, these people had a collective name Johns, so why must they be "John"?

At that time, there was a very famous song that sang "Johnnie get your gun". From this, John used to refer to the soldiers. Moreover, in Europe and the United States, "John" is a very common name, and later in many proverbs, "John" is also used to refer to men. In recent years, with the strong voice of equality between men and women, "Dear Jane letter" has been born to refer to the letter of love written by men to women.