Would you mind including more details. Id love to help you once you update your post... Thank you!
I would say c, but I could be wrong.
Answer:
Select the shapes to be merged
Explanation:
Just did it on edge :)
Probably their amazing sculptures.
Actually, the civil war make their relationship became much worse.
Because of the civil war, the ally has to lose a lot of resources for war supplies and equipment. This led to a situation where the allies no longer able to pay the treaties that they promisd to pay to the Sioux, which eventually ended up in conflict between the two group.