[quote=GreivousKhan]
That really depends on who is currently the leader/Harbinger, the reason they did not take part in the civil war was largely due to political reasons. No where is it ever said they can't get involved in a war, that would be missing out on an entire market for them anyhow.
[/quote]

+ With Skyrim unified , they would also fight for the greater good, aka to preserve skyrim 

(Sounds cheesy, but it's true )