"I do not pretend to write much of a letter. You know under what circumstances I am writing"

Joshua Chamberlain was a Union Army officer throughout the American Civil War. In this quote, he is expressing his difficulty in writing a letter due to the scenarios he is in. He is likely describing the war, as he was a soldier at the time. He is likely in a difficult situation, either in the middle of battle or in a challenging environment, and is not able to compose a prolonged letter. He is most likely attempting to describe to the recipient of the letter why he is not able to compose more, and is excusing the brevity of the letter. This quote reflects Chamberlain's devotion to his task, as he wants to put his own requirements aside in order to fulfill his obligations. It likewise reflects his humbleness, as he wants to admit that he is not able to compose a longer letter due to his scenarios.