Yay! I started a new game and I managed to win (sorta). I managed to make peace with 3 AIs and then defeat the other two, so I count that as a victory. However the game didn't end which tells me you can't really have a peaceful victory :-/ (I seem to remember that I managed it once though)

The trick for me was the map, if you can get a bit of isolation and you don't begin smack in the middle of 3 others, you have a chance to avoid them until you can convince a few to join you. I actually gamed the AI a bit by not taking a planet very close to me because, as some noted here, that would give me a planet within 2 jumps of an AI planet, which means that everyone else would ask me to go on assault missions. By avoidiing to colonize that planet (even though it was a juicy terran) I managed to get far more resource quests which allowed me to find allies.

Had some awesome battles too but my VGA stopped to a crawl from the amount of ships and particles.

Now to arrangle a nice 3v3

Come on, it's fun stabbing them in the back!

Not quite. Between Cinematic Mode and Ctrl+Shift+Z to remove the hud, you'll get a fairly clean view of the action though.

Semantics : I'm going to stab you now, with bullets

Don't know if this helps you out bigdog, but I had problems fighting vasrai also with advent.  I once saw a evacuator capital ship not only survive, but have their HP continually heal and rise during the course of one battle due to their Overseers.  That was pretty incredible and frustrating to watch since I focus fired from about 60+ ships. 

Anyway, priority targets should be Overseers and Subjugators.  Overseers heal and those subjugators have a disabling ability with an area of effect.  Very bad for your fleet if they come in large groups.  After that I usually target the capital ships.  I usually ignore the cruisers until clean up, because they tend to get inside my fleet's formation.  The guardian's push ability is good to use if you've got it researched here.  For my capital ships a choose a radiance , a progenitor and I forgot the name of the one that has Vengeance.  I keep alternating animosity between capital ships if I have multiple Radiances.  I'm sure the damage return helps in battle, but I've always been more interested in just not having my smaller weaker ships shot at to keep up the DPS.

In a recent game I had none of this was enough and ultimately what I had to do was get them to attack a planet with 35 defense platforms.  I managed to jump into gravity well from one side that put them beween my beam cannons and the fleet allowing me to cut them to pieces because in order to fire at me they would have to turn away from the cannons.  Most of the time AI will attempt to leave the gravity well if this situation occurs, so make sure to build phase jump inhibitors and use a small fleet of subjugators to to disable their jumps to keep them in the gravity well for as long as possible.  You can slowly wear down their fleet this way, by leaving your fleet out of that gravity well and luring them into attack.

Hope some of this helped.

The problem here is that you were focus firing your entire fleet on a "tank" - a cap ship with full support is very difficult to take down because it has a lot of hull, gets full benefits from ~70% shield mitigation while being repaired, and your dps was probably suffering from the Stilaktus Subverters disabling your frigates and cruisers.

the way to attack a Vasari fleet late game, provided your fleet is at least of comparable strength (if they have 3x more ships than you do in terms of resource cost, your are most likely SOL anyway) is this:

1.  Focus fire on the subverters ASAP.  They will probably be "mingling" with your ships due to their "teleport and dsiable" ability, which should make them relatively easy to pick out.  Take them out to the exclusion of all other ships - the group disable SEVERELY cripples your dps, but the subverters are fragile by Vasari standards and should go down in one or two salvos each if fire is concentrated - this also means they won't have time to gain benefits from support ships before being pulverized.

2.  Once most of the subverters are taken out, you have a choice to make.  If it's a mixed fleet, start trageting overseers, if it's an LRM-heavy fleet, start taking out the missile ships by focus firing a couple at a time.  The LRMs are fragile enough that they won't have time to get healed if you focus fire them.

3.  Take out the overseers if you haven't in step 2.  If you have, take out the cap ship with the most annoying ability (probably the Carrier Cap Ship with repair cloud).

4.  Mop up.  If cap ships are a problem (i.e high level), take them out by focus fire.  If the cap ships suck, take out the karrak assailants, heavy cruisers and karrastra skirmishers in that order (LRM -> heavy cruiser -> light frigate).  Adapt this based on circumstances (if they only have a couple heavy cruisers mingling with your fleet, while the LRMs are sitting at range, pick off the heavy cruisers, than move on to LRMs, etc)

5.  Kill the carrier cruisers last.  Never waste your time shooting at carriers unless you are picking off remnants of a retreating fleet, or your opponent has nothing but carriers.  They don't do any damage directly, have a large amount of shields and hull (meaning they get a lot of benefits from shield mitigation), and even when you kill them, the fighters/bombers will linger for another couple of minutes.  Counter the fighters/bombers the best you can, and focus on ships that damage you directly.

Having a couple of Radiance Battleships (since we are talking Advent) can be good here - the battleship has a very synergistic set of abilities.  Use Animosity to make the enemy attack your tank (Cap Ship), Ablative armor will passively restore your antimatter (while reducing DPS slightly due to the armor bonus), which you can use to detonate animatter in surrounding enemy ships, doing both decent DPS (albeit spread out, and so subject to repair cloud) and preventing the subverters and overseers from doing their thing.  Cleansing brilliance is nice if your ship is that high, but really, the three primary abilities shine if used together.

Ok guys be realistic. srsly now how can a game with only hard AI's be all that difficult. when I play single player I set it up on a random huge map some times multi star with all hard AI's and locked teams some times(if I'm feeling praticularly machostic) and I come out looking like a porn star. I wipe out the first 2 AI's next to me in like the first 45 minutes of the game. honestly can you guys explain in more detail why you can't seem to win cause.

There are thousands of strategies out there and one thing you can do to ensure a victory is make fleets and

Yeah this map was a good lesson for me. I went back to about the 4 hour mark and focused more on politics and fleet building. I was able to declare peace with three factions (up from 1) and it gave me the time I needed to augment my fleet and wipe out one of the Vasari. Now I'm free to do some planet capping and maybe take out one of the three remaining factions.

Biggest challenge is still those massive Vasari fleets. Good thoughts from Drunk Templar about taking out the subjugators before the overseers.