Take redlining for instance. That happened a long time ago. Redlining systematically and intentionally deprived non-white families of home ownership, while helping white families to own homes. But wealth begets wealth, so owning a home lets someone borrow money against it to start a business. When these people die, their children will inherit their wealth. As a result, the (grand)children of a family are still denied opportunities that they would've gotten, if not for redlining.
The creator of VeggieTales has a great video on this! https://www.youtube.com/watch?v=AGUwcs9qJXY
P.S. Yes, a family who was able to get a home loan (redlining didn't affect them) might have squandered this wealth gambling, or maybe they didn't pass it onto their children, so some people unaffected by redlining may still end up in a similar place. Similarly, some families that were affected by redlining have still managed to accumulate wealth in spite of redlining. My claim is that the family that squandered their money still got the chance to squander was was given to them, and the injustice is that the redlined family was denied that opportunity.