Writing. Writing was a huge game changer compared to 4000 BC. A quick search says that the first we're relatively sure about was around 3200 BC. I mean, sure

Writing. Writing was a huge game changer compared to 4000 BC. A quick search says that the first we're relatively sure about was around 3200 BC. I mean, sure, in 1000 AD most people couldn't read or write. But enough could to coordinate activity more closely over a wider area than possible without it.