there is wayyyyy too much to talk about a 6 v 12 war.
to keep it extremely simple, 6 is at a huge disadvantage right from the start. the gold is slow which screws you early game, there isn't a lot of room to build inside the actual base, there's not a lot of wood close to the town hall or where most people typically make their lumbermill which slows wood flow down, and 6 is easily towered.. if the tower is successful, it's pretty much pointless to keep playing in a 1v1.
the best way to beat 12 when you're 6 is to have a good idea of how your enemy plays, and know how they play vs 6. If their opponent is 6, do they do a super massive rush because they believe it will be easy to out rush 6? do they really love towering people? do they want to play it safe and choke 12 o clock with 6-7 grunts and a cat?
If you suspect 12 will play safe and go 6 grunts and a cat.. maybe stop peon production around 12 peons, go mass grunts, and get an unseen cannon tower @ entrance of 12 o clock before their cat pops... or maybe counter dual and put a ton of defense up at the right time (just before you expect him to run in you with lust) .. with the idea being that you will be slowed to lust, but once you get there you can overpower 12 because 2 hall > 1 hall.
If you think they will try to overwhelm you with grunts .. you can either turtle and make a cat, or slow peon production to match their grunts .. and after their big wave fails run up with your grunts and a peon or two to cannon your way into 12 .. again, idea being they don't know they're being cannoned.
regardless of whether they love towering or not, you need to make sure you're not towered.. whether it's building farms back there, patrolling with a grunt, walling it off with a smith/farm like some people do.. whatever works and makes you feel the most comfortable
The advantages of 6 o clock (if you can live long enough to utilize them) is 8 is an awesome easily defendable expansion. s9 is a good early decoy expansion and can also serve to make sure 9 isn't taken by enemy (make a dk in s9)
also .. 6 is typically the very last place scouted in 1v1 because it's the smallest threat... it's comforting knowing you're safe the first 2-3 minutes of the game
here's a couple video's from 6 o clock.
VIDEO
< me vs pavlos
VIDEO
https://youtu.be/iCEDBxaWXro?list=PLxMYE5H6_03KKg_JAHcZEa629gPbuJiIo < viruz vs braviet
VIDEO
< me vs frost (actually a 6 vs 12)