I seem not to being able to edit above post, sorry for that long link that I wasn't inteding to put there

I just noticed how much I was abetting a threadjacking; apologies to GJDriessen.

In my current TA game (tech trading off), I'm finally learning something about fighting off early success by the Korath. The spore ships that help them claim all that territory are also their weakness. A spore ship swarm leaves a swath of barely populated planets in its wake.

You just need to fend off or destroy the Korath warships and a single fleet of 4-6 transports with 2000 troops each can take a beach-head system or two. If you have a good econ, that beach-head can quickly start sending out partially-filled transports that are more than sufficient to take worlds with just a few million Korath on them.

I usually pick on the weak civs - the ones that for whatever reason lost out in the colony race. They're usually way behind on tech, and their homeworlds are going to be valuable.

I don't declare war that often. I just construct a military starbase with all the ship boosting bonuses right next to their homeworld and stockpile the necessary ships and transports. Almost invariably they'll trigger the war, even if it is suicidal. If they don't, I get to attack when I'm ready - which means a civ that never pread beyond a couple of systems will probably die in one turn. Avoids any irritating surrenders. Strangely I often seem to get the "We can see those transports" war triggered the turn after I've declared war. Always feel the enemy isn't quite up to speed there - in extreme cases it looks like they've managed not to notice I've already conquered them.

I sit back and wait.  When i do get wardecd, i will fight (if i can) till they are wiped off the map.  Another way i collect planets, is to periodically offer to buy planets, you might be surprised as to how often the AI is willing to sell.

I goofed another one !

I did not pay too much attention to the races selected since I am still learning the GalCiv universe. now the following happened:

I play Arcaean and I selected the game mode where only military victory works (no tech or aliied/influence allowed). I am in a position to murder anyone and have gobbled up humans (hate them anyways) Yor and 2 minor civs.

The Torians and another civ were my allies until I was sure I could win - then I took down the other civ (break alliance, attack, win as I expected). Now I am allied with the Torians and probably since we are "team" from day 1 I can't cancel the alliance. Either I am too dumb to find the button - it is not where it was for other Civs - or it wasn't intended.

Since the only Victory condition left is "last man standing" I probably shouldn't have picked Torians for my Galaxy. Now the only course of action I can imagine is to grab planets by flooding them with influence bases.

Is there a way to break up Alliances pre-determined by race choice ? If not, it seems odd that I did not "win" considering only me and my eternal Ally are left....

It sounds like you might have figured out how to make an "unwinnable" map. Starting a game as part of a Team does mean that you have a permanent alliance (or alliances).

Have you tried just attacking the Torians? I have no idea whether the game would let you do that with your setup.

On a Gigantic map I have been able to buy out my last opponent's empire (I don't remember the exact number of planet but it must have been quite a few) only because I had ridiculous amounts of money from a tourism mega-event.

"Unwinnable" ? Not quite... Confusing ? Yes.

I tried to just attack the Torians and got the message that in order to do so I should break my Alliance first. This indicates that it was intended to be possible.

However, I am still unsuccessful to figure out how, maybe one day I find it.

In the meantime I did what I suggested above and built several Influence Bases around their planets. interestingly the Torians then started sending fighters and transports to their and my worlds. But they never attacked or broke the Alliance, so the purpose may have been just for show or to represent.

In the end their planets just converted to mine and I won by "Conquest". I still doubt this was the best way though since I needed many turns to accomplish this "diplomatic" victory while copnquering them would have taken maybe 10.

If someone figures out how to break a "Team" Alliance, please post here.

I'm not afraid to fight the strong guys at all, if that's who my neighbor is.  It's hard to bribe other civs to attack them, so I'll just do it myself.  Just being at war forces them to focus more on military rather than extending their lead.  Since all his ships tend to come at you from one direction, just get a military starbase and fleet up.   I'm not terribly worried about all the other civs--just a few bribes, and they're all at war, too.  What's gorgeous about fighting strong civs is, the tech stealing.  So, your military advisors insist on not trading us Harpoon?  That's fine....  Weak civs don't have anything I want.

I also need to spy around and see what planets I want.  If I see a precursor library, that may well decide who
I want to fight.

Team is, by definition, unbreakable. Winning by influence flip was your only option.

I generally look for someone who I have a sizeable height advantage over, and who appears to have realtivly low upper body strength.

I generally weaken my most powerful enemies with combination of prolonged espionage and engaging all their neighbors in war with them. Just as they are being overwhelmed, I swoop in from behind their lines using a massive fleet of long range transports and quickly conquer all their worlds in a matter of weeks. The trick is to accuratly predict their weakness. The best sign I've noticed is when their fleet begins to retreat back to their borders in attempt to efend their failing lines. It can take a long time to prepare for this by making scores of combat transports with huge hulls and moving them across the map to the rear of your enemy, but victory is nearly assured. Then there is the matter of the weakened less states.....muhahahahahaa! Resistence is futile! 

Yeah, I often bribe the strong guy to attack somebody else, and then I turn around and attack him while he's still at war.   I have to pull my spies from his planets, though--he'll use the money I just paid him to nullify my agents.  I need those guys to nullify his morale buildings ahead of an invasion.  No matter--I just care about getting Medium or High espionage level, so I can track his ships.

Now there's a possibly neat feature to help with the >20k problem: independant, hideously expensive assassination contracts good only for spies on your turf--kind of an analog to leases for ship purchase or upgrade.