Hi, Azz,
a. As our enemies are joining forces, so should we.
b. We should join forces as our enemies are.
c. We should join forces, as our enemies are.
Which could mean
We should join forces because our enemies are.
?
I think they could all mean
We should join forces while our enemies are.
We should join forces in the same way our enemies are.
Is that correct?
Many thanks.
A is the best one. I don't like the way sentences b and c are formed. Instead of 'b', I feel that it is more natural to use either:
a. We should join forces just like our enemies.
b. We should join forces as our enemies do.
In all cases, with no further context, both readings (while / in the same way) are possible.
Concerning your example C above, I see that 'as' has only one meaning here: 'because', but the whole sentence doesn't sound quite natural to me. I'd better say, 'Our enemies are joining forces, and so should we.)