You want to play as New Cannan!

You have to in the end, go to war with the White Legs & lose to the White Legs. You can achieve this in anyway you like. But there can be a step to step process to it!

Well in the beginning, it's practically just going afk for a bit. Of course you gotta do some things in the focus tree first. You of course want to do the first 4 focuses of the focus tree. Then select "A Growing Threat"

Then you basically do whatever till a civil war/uprising starts.

However you may fight the civil war w/ the Brigham Barons. Win the fight!
Then you will have a conflict w/ the Farfield Warband. As before, defeat them.

At this point, you don't really do anything besides wait for the time to tick down. You will of course get events like the followers of the apocalypse. Your choice what you do w/ them. You can do some nation building but not much is gonna happen for you. You mainly are waiting for it to be the date 1 Jan, 2279

Around the 12th of Nov, 2276 (12, NV, 2276). The White Legs will start beginning their territorial expansion. Thus their threat level will increase allowing you to do "Attempt Limited Rearmament" in your focus tree. And then a few other focueses will become avaible.

Eventually the White Legs will start consuming it's neighbors.
All you have to do is wait for them to win their wars. You just sit back and wait for them to be on your doorstep.

Once the White Legs conquer the Tar Walkers or the White Legs border you.

You will receive a popup newspaper. Then a focus ("Barbarians at the Gate") should automatically be finished. Wait for it to become Jan 1 2279!!!!!!
Once it is Jan 1 2279.Go to the focus "Bring the War to the White Legs", and start it.

Once you finish the "Bring the War to the White Legs" focus. You should be able to declare war on the white legs. Then make a fallback line behind New Canaan. After letting the White Legs walk around in your land for a little bit. The "Canaan in Flames" focus should finish. Then you should get a popup. Joshua should be able to become a general at this point.
Then let the White Legs win the war against you. Once that is over, you will be moved to Vermillion Cliffs.

Now you should a little bit later get a popup. Basically asking you if you want to have "The Burned Man" become your leader. You should select "The Burned Man is our new hope." Then Joshua Graham should become your leader!