There's not a hard and fast rule among universities or historians in general to consider events beyond a certain number of years "history" vs. "current events." One only has to look at Mao Zhou Enlai's (probably apocryphal) comments on the effects of the French Revolution being too recent to analyze to see an example of this.

That said, we do have a 20-year rule fairly explicitly to avoid discussion of modern politics and modern events ... and as we inch closer to Jan. 1, 2021, we are semi-seriously considering extending the deadline to avoid 9-11 conspiracy theories.

This rules roundtable explains the reasoning behind the 20 year cutoff, both on the pragmatic side of things (we don't want to endlessly analyze every past US administration in the light of the current one) and the philosophical (at what point do we actually feel we have enough remove from a topic to engage with it).

To sum up, 20 years is arbitrary, but we don't think it's capricious in what can and can't be discussed, and it functions pretty well in keeping modern politics out of the subreddit.

With somewhat more than 900,000 subscribers and slightly less than 40 mods, we can only do so much in the time we're given, and removing modern debates lets us focus on, well, history.

There is also a debate among historians that time does not really matter in the sense that doing history is a way of thinking about different topics. So the only thing that changes is the nature of the historical material that one must investigate. For example, newspapers are a very popular source for historians, or digital data, etc.

I don't know if I can answer this but I gotta congratulate this sub for implementing this rule. When one sees the debates at other social media or even other subs it's alarming how events just from 10 years ago still sparkle a lot of biased debate. ¿How could Obamacare be measured in just 8-10 years? ¿Can we really explain fairly the european migrant crisis? ¿How about even the post 9/11 world? It's going to be soon 20 years of 9/11 but I doubt the conspiracy theories will end anytime soon.