I would try to ally, then try to culture flip them.

You know, I'm getting tired of people calling every solution other than a military one "cheese". Honestly its a good tactic. Diplomatic and culture wins can be just as tough as military ones.

But if you are dead set against anything but a military victory, then I suggest you launch a sneak attack deep in the heart of their territory. Hit their major production worlds, and even their home planet. Hopefully you can snag some advanced tech and be able to create some custom anti-Korath ships. Just be sure you have a good strong economy to support a prolonged war effort.

Hi!

Why cheese? If you can't beat them, join them.

BR, Iztok

Hi!

Before that happens be prepared to become a vulture: wait with lots of troop transports at the edge of the front and when enough victim's planets lose defenders, you land your transports and claim planets for yourself. You even don't need your own military, as the attacker will take care for victim's warships. That's not a honorable tactic, but c'est la guerre.

BR, Iztok

The sneak attack option will only work though if you don't have neutral ground enforced, because if it is, all your ships get put on the border, very annoying.

On a side note, how do you get another group to attack someone? Everytime I go to war, I want to ask other civs to join in. I go to the diplomacty screen, choose attack, but no one's ever in there, even if the two civs in question hate each other. Am I missing something?

Cheese tastes good... hmm wrong cheese?

Yeah, you might have dug yourself a hole actually. By getting other civs to fight the "superpower" and giving it the chance to expand its territory you have made your position worse. What you need to do is fight their population, not their army. There are several ways to do this (cheesy or not):
- Gain more territory yourself so you can out produce them. By gaining more territory, you will gain more population. One of the best ways Iztok just described. The AI is slow and inconsistent about taking worlds (the Korath, are sadly the exception - because the AI is released from the burden of worrying about population management, and can just kick out spore ships) - and if you have a few dozen extra transports sitting arounds, just take every world they clear. You know the civ you are taking the worlds from can't fight you, their military is devastated by the Korath. Timing is the key to this strategy, you might only have a window of a turn or two to strike each world.
- Use spies on all of their farm buildings. This works better than you might think, if you can manage the money for a decent number of spies. The AI doesn't build a lot of farms, and the Korath in particular have lots of worlds (high maintenance costs) and small populations (so small taxes). Keep them struggling to produce troops and taxes by forcing all their worlds down to a 6b pop cap.
- Culture flip the Korath, make their populations come to you. It is SAFER to do this if you ally with them first, but not necessary (and maybe not possible depending on your alignement and diplomacy skill).

They key is you want worlds and people - military might can come later. If they have 60-70% of the galactic resources (that is planetary tiles, not minable resources) then you have probably lost, although there is still a sliver of hope. If they have less than that, there is still time for you to use some method or other to pick up as much territory as they'e got and compete.

Go go 50 moves/turn transports!

Seriously, cheesey as hell, quicker than culturebombing. Got screwed over a few times myself, and leapt from 4th to 1st in economy and social in one turn thanks to some well placed attacks. They then gave me their two biggest planets in exchange for peace, and my military started skyrocketing.

Also if you want open war, try moving your fleets around with allies fleets for backup. If you can't take them on yourself, pounce when they're weakened by someone else.

Also, high defence dreadnaughts are a risky option. They can ruin your economy but single-handedly take on battleship fleets if you've maxed out the defence tech.

Bunker down with military starbases. Do that right and they pretty much carn't touch you untill your ready to come out fighting.

Once a superpower reaches it's military tech limit, you can only get stronger while they get nowhare!

Tell that to the Von Trap family!!

hehehe tell that to the von trap family too!!

Hi!

You have to check what they think of your race. You can find that in the diplomacy window under the third tab. IMO the main obstacle is the "-- your military strenght", that cancels out the "++ your diplomacy skill".

BR, Iztok

I find culture flipping not done as well as it should. For starters, it's easy. Research two quite cheap trees that have their own bonuses outside the culture goal, and then start building conships to build influence starbases. Secondly, I hate it when it happens by accident. There should definitely be some kind of slider for influence, because right now, you're culture flipping while building up your military/heading for tech victory/whatever with no downsides.
And as for alliance breaks for culture flips, bad idea, because culture flips happen by accident. Alot.