If I was to study one period in history (didn't study the subject at school) that would give me the biggest insight / impact, which would you recommend?

Writer - markfielding.xyz / book club & tech v culture Podcast - Thinkingonpaper.xyz 

Writer ✍️ paragraph.xyz/@driftless | Creepy stories 👁️ unnerv.ing | Poems ⚡️ /writers 

So the old adage that history repeats itself is valid? Study one and you study them all? I've always wanted to know more about the Mongols and the vikings and how they were similar/different.

You can’t study one period and get much insight. What’s insightful is seeing what is consistent or unique across different periods.

That said, WW2 and the decade after is a good start. Myths of that period color so much of our current moment.