How does wealth and income inequality increase over time?

So I've seen plenty of graphs pointing out increases in wealth and income disparity, but I don't exactly understand the process in which it is happening. Is it because the largest incomes come from investments and loans that money gets wrapped up in? Is it the natural effect of international trade and people of other countries like Chinw gaining a lot of wealth? I have taken basic macro/micro economics(which is still cramming graph memorization for a few months), but I don't have a clear understanding of how this happens or how to fix it, or if it's not the real issue and just an obvious target. Thank you for reading, I appreciate any help you're willing to give.