The AI didn't attack me on hard.

[chaoswar]

I played some game on hard difficulty. In about the 260-300 turn,
the AI didn't attack me. It declared war on me, but no attack. And the races didn't attacking each other.
I turned off the Mission.
Scenario was normal. Difficulty was hard.

Well what's happening if I am not attacking?
My empire, and techs were lower then the others so I am not declared war.

[Zaimat]

Typically if you are at war and they aren't attacking you it is likely they are fighting elsewhere/another enemy or building up their forces (if you are stronger).

I can always take a look at your saved game, if you can send a report. Please identify which saved game in your report so we can check the right one.

[sara736]

Do the Varians need to be in a war with the Har'kun also when they beg for Mercy or just me? What is the exact message I should be looking for to finish the quest?

[null]

Do the Varians need to be in a war with the Har'kun also when they beg for Mercy or just me?

Should work with any diplomatic condition. So long as they actually surrender to you.

What is the exact message I should be looking for to finish the quest?

I think they will always use the word "surrender" in the missive. Pleas for mercy are just requests for peace.

From the man himself:

Their relations doesn't matter but you need to get the Har'kan to surrender to prove your worth to the Varaians. If they beg for Merci or sue for peace and you accept that's not the same, keep refusing and put pressure on them (blockade their homeworld or last remaining colony) and eventually they will lose hope and surrender.

http://forum.l3o.com/viewtopic.php?f=7&t=1243

That blockade tip was super useful for me. I was resorting to demanding embargoes from other powers and sending in small ships to bombard their last colony down to within a handful of guys. No dice, but parking a big fleet over their last planet to blockade for a few turns did the trick.