No Stupid Questions

I noticed that in the USA people are often strongly divided based on whether they identify as being "black" or "white". Basically many people there make this a big part about their identity and separate communities based on it to the point where they developed different cultures and even different ways of talking and behavior solely based on whether they identify as "black" or "white".

As far as I understand it's based on the brightness of their skin color because of slavery but it's not quite clear to me who is considered "black" or "white" since I've seen many people who for example have very bright skin and seem to have almost no African ethnicity but they still identify and talk/behave as "being black".

I wonder why they still have this culture and separation since segregation ended in 1964.

Because in other regions like South America such as Brazil for example this culture doesn't seem to exist that much and people just identify as people and they talk, behave and connect the exact same way no matter the skin brightness. People such in South America seem way more mixed and seem to not have this type of separation like in the USA based on external features like skin, hair or eye color.

To me it kind of feels like this is a political and economic reason in the US that they purposefully want to divide people for their gains. Because the extent to which this seems to have been normalized in Americas every day conversation both in private and in public/commercial spaces feels like brainwashing. And I wonder if this will ever improve since it seems to go as far as people being proud about these racist stereotypes and think this is completely normal. But considering the broader global context and America's historical background it doesn't seem normal. Especially with Americas context of slavery you would expect there to be strong efforts of fighting these stereotypes and having a political leadership that doesn't see "color" and only judges based on individuals personality.