I don't think this was the British. (Not to apologize for them - they certainly made things worse, not better.) Sudan sits on a historical chattel slavery route that stretches back to Roman times. It's hallmarked by the Northern population raiding the south, along racial lines.

Scholarly article for reference if you want to learn more: https://www.jstor.org/stable/827888

Let's say that all of the problems in Sudan are the fault of British colonialism. (I don't think that's completely correct but just for the sake of argument.) The British are gone and not coming back in any significant numbers. Now what? What is the solution?

A typical British colonial strategy was to ally with a minority ethnic group. The formerly downtrodden minority group now got to be the leaders, but, being the minority, they would stay dependent on the British, else the majority would rise up and kill them. In the post colonial world unfortunately that is what happened in a number of cases.

Sudan was under British rule and Cyprus was under British rule at the same time. Outcome is vastly different. The Brits brought civilisation and made Cyprus what it is, enabling its current prosperity (only difference between Cyprus and Greece is that Cyprus was a British colony and Greece wasn't). Somehow it didn't happen in Sudan.

And no it's not because they handled locals differently. They didn't care about locals. Colonialism is about exploiting territory, not population - locals, for colonialists, just "happen to be there" and are usually an obstacle or annoyance rather than a resource to exploit.

Maybe it's because locals were different.