4K doesn't really say anything about image quality, just the resolution of the picture, which tells you the theoretical maximum level of visual detail.
Focusing on resolution is like asking "how strong is one meter of rope" without talking about the composition of the rope.
With streaming video, image quality ultimately comes down to the codec and the bitrate. They probably use a relatively low bitrate regardless of codec.
Much of the "wealth" was the people they enslaved, so they did not get to keep it. The American Civil War is seen as a huge and enduring economic loss (but moral gain) for the southern states.
The population of France is about 7.5% Muslim. France has had a close relationship with the Muslim world since the 19th century when they colonized parts of North Africa and the Middle East. Sadly, the position in French society of colonial immigrants and their descendants is not very high. Also sadly, France has had a lot of experience with this sort of violence, both in the colonies and "at home".
If you know the attacks were carried out by Muslims, there's no reason to assume these attacks were carried out by refugees.