[Destro]

No, it is correct. The current ones are the descendants the ones that gave the Brits such a hard time were ancestors.

[Max Combined]

"No, it is correct."

No, as it is written, it is incorrect.

The relative sentence, is written as follows:

"Its population of 900,000 people include the ancestors of tribesmen who in 1920 launched a ferocious rebellion against British rule."

Its current population of 900,000 people cannot include the ancestors of tribesmen who gave the Brits a hard time in 1920. The ancestors of the folks who gave the Brits a hard time back in 1920 were around even earlier than 1920.

It is the descendants of tribesmen who in 1920 launched a ferocious rebellion against British rule who now comprise a portion of the current population of 900,000 people.

It is not too hard to understand and I have to question your reading and/or logical abilities if you cannot discern the difference between descendants and ancestors even when it is pointed out to you.