Sentence Structure

[Ofriendragon]

How about the two sentences? If they are not right, how to correct them?

a)That the skills to make copper and bronze objects spread to Britain was through war and armed conflict.
b)It was thought (that) that the skills to make copper and bronze objects spread to Britain was through war and armed conflict，...

Thanks in advance.

[Tdol]

You can make the second neater:
b)It was thought that the skills to make copper and bronze objects spread to Britain through war and armed conflict

[Likeguslee]

That the skills to make copper and bronze objects spread to Britain was due to war and armed conflict

It was thought that the skills to make copper and bronze objects spread to Britain was due to war and armed conflict