Hello!

Our subreddit exists for basically one purpose - providing high-quality, in-depth answers to people's questions about the past. We've found that in order for this to work on Reddit on any significant scale, the subreddit needs to be heavily moderated. Fundamentally speaking, this falls into two categories.

The most common thing we moderate for is answer quality. We aren't interested in a link to Wikipedia, we aren't interested in guesses or something you saw once on TV - we want quality answers from people who know what they're talking about. We expect users answering questions to be familiar with up to date scholarly literature on the subject, and remove answers that don't meet this threshold. We've found that unless we remove low effort posts, users with the required knowledge won't answer it at all - it takes hours for good posts to be written sometimes, and no one is going to bother if no one is going to read past the bad puns at the top of the thread.

The other side of the coin - which you are asking more directly about - is ensuring that the questions that get asked are answerable in the first place. A lot of questions about the past can't actually be answered effectively according to our rules. Sometimes it's because they are too broad, or because they are phrased to be inherently subjective - "who was the best king ever?" fails both of these, because no one has detailed knowledge of every king throughout history, and 'best' is going to depend on your opinion of what makes a good king. Our rule of thumb here is whether it is reasonable to expect any one person to have the knowledge to respond to the entire question - if not, we ask the questioner to narrow it down or otherwise rephrase it. Some questions are at the other end of the scale - they are so basic, depth is not possible (we do have a weekly thread for 'Short Answers to Simple Questions' for this reason).

We have also developed rules over time designed to ensure that the subreddit functions well. We don't allow current events or contemporary politics (all questions must concern events that happened at least 20 years ago), or questions that are otherwise seeking to moralise or push an agenda, as the ensuing discussions tend to be unproductive, and historical methods aren't best suited to the immediate past anyway. We also forbid direct homework questions, because our expert users don't want to spend their time doing other people's homework. We also reserve the right to remove questions that cross the line, accidentally or not, in terms of bigoted content, because we don't see that it has any place here, and again runs contrary to our mission of attracting a large and diverse range of questioners and answerers.

This isn't intended as a list of all our rules, but rather an overview of the most common stuff we do as mods, and why we do it. Hopefully, it makes sense to you. If they or our wider mission don't sound appealing, that's fine - we accept that this subreddit isn't for everyone. You are very welcome to make use of the rest of the internet, including less moderated spaces on Reddit such as r/history or r/AskHistory.

It was explained by the moderators:

Hello. Unfortunately we don't allow eliciting of opinions here. If you'd like to repost the question looking for just historical accounts and reasons, that would be alright, but as it's worded right now it's probably better to ask at r/history or somewhere similar.