AskHistorians seems to believe pretty strongly that this letter never happened, which may be obvious to people familiar with the story, but I'm hearing it for the first time in the context of this HN post. :)
A good thread on the history of, uh, stern Russian responses to threats:
A good thread on the history of, uh, stern Russian responses to threats:
https://www.reddit.com/r/AskHistorians/comments/e1qciu/in_re...