United States - Postal Service

Do you remember that in February I participated in InCoWriMo, the challenge to write a letter every day of the month?
Today I received this returned letter from an US address. I have to admit that I am not surprised that the letter has been returned, I am surprised of the state the letter has returned to me! It seems that has gone to war! Inside there were just a letter and a postcard, nothing else. Why is it so damaged?

At the rear of the envelope there is this apology...

This has never happened to me before, and I've been living in Spain, UK and Ireland... this is not something that you expect when you send a letter or something that I've never thought it could happen! I've "lost" some packets before, some of them I am sure were stolen, but a letter is something personal, not a money value, how can someone treat it like this?
I am always surprised how people treat things...! Have this ever happened to you?