What was to be done means that they couldn't have done anything to change the situation and you cannot use how could we do in its place

And riding on the ridge of waves means doing something risky to get fame . It can be positive or negative depending on the sense you are saying it.

If someone is doing something kind of bad to get fame they would be called to be chasing clout. If someone is doing something good ,like positive tactics , we say he is trying to increase traffic.

Let me try to explain it in a simple manner. You know a sentence structure is ' main person (noun) + rest of the sentence ' so here The rebels (the subject or noun) crossed the region , pillaging and Looting as they went. I can go into details like subordinate clause and how it works but you would not need it to understand this prblm now. And after all it makes the sentence sound more beautiful and wholesome. Any more queries , just text me. I would be more than happy to answer. Don't have a good day. Have a great day. 😊☺️

It’s cold.

I really admire Doctor Yuan Longping，who is known as “the father of hybrid rice”. He saved many lives by increasing the production of rice.