[YmolafBp]

When did this idea come about? During slavery times?

In Western society it started with slavery. People would use as an example of Black slaves not being intelligent is that they'd often break their tools. This was done on purpose in many cases as a way of saying, "go fuck yourself, Whitey" but it was perceived as stupidity. It also didn't help that they didn't speak properly, which is expected. They adopted local poor White dialects.