A while ago I made a writeup for how Fortresses work. its still up-to-date:
viewtopic.php?f=113&t=35455
under the "beginners survival kit" sub forum you might be able to find some good guides for topics like this.
if not,
T2 and T3 zones doesnt really matter too much on what realm locks them, they will push a zone in the racial pairing one tier up. For example a zonelock in T2 Dwarf vs Greenskin will open up T3 in that pairing. These zones have a lack of appeal as new chars outlevel the oRvR influence too rapidly to grind and use the gear obtained. These T2+T3 zones are mostly just speedbumps for the campaign, and can serve a use for picking up the playerkill-quests in the Warcamps to getting Seals for your 3day +25%renown potions (purchased in capital)
When the campaign reaches T4 zonelocks and momentum start mattering, if we use the example of T3 Dwarf vs Greenskin racial pairing. If T4 Middlezone of Thundermountain locks the racial pairing will be pushed closer to the loosing Realm's fortress by one T4 zone. So Kadrin Valley if Destro locks Thundermountain, or Black Craig if Order locks TM.
In Order to reach a racial pairing fortress several zonelocks must be reached by the same realm, on top of that, in order to besiege the enemy Capital 2 full T4 racial pairings must be won by a realm and the fortress lords defeated! (Dwarf vs Greenskin (1) Highelf vs Darkelf(2) Chaos vs Empire(3))
So how do you lock a zone?
Captureing two battleobjectives and holding them, will make resource boxes spawn on the Flag on the BO. picking these boxes up and turning them in at the flag on the bottomfloor of your realm's keep in the zone will give progression to build keepranks (yellow bar on the keep on the map)
After reaching 2stars you can spawn and deploy a ram from your inventory, if you have purchased one at a siege merchant and I do think there is a requirement to be within a highrank guild to deploy the ram(?) Bring a couple of singletarget canons along with the Ram and drag the siege weapons to the enemy keep.
If a ram is destroyed it has a 10minut respawn timer, it can decay if left unattended by the player spawning the ram leaving it behind or too far away. Canons have more ammunition applied to them as more resources are turned into your own keep while siegeing.
Enemy players can deploy an Oil cauldron at outer and inner keepgatehouse, after each oil is destroyed it has a 3min cooldown exactly before it can be redeployed. Compared to Offensive siege weapons that have endless uses, an oil cost 5gold and is gone from your inventory when used.
After succesfully breaching outer gate and inner, battling the keeplord and clearing the keepfrom defenders the keep will turn into a "ruin" after the lord dies. Meaning keepdoors will no longer respawn no matter what. Defenders cant deploy any oils, but do have the option to spawn rams at their warcamps now instead of their lost keep.
To lock the zone, one realm must controle their own keep/ruin + enemy keep/ruin and 3/4 battleobjectives.
The live vision of RvR campaign, mostly still correct with some changes on RoR
https://www.youtube.com/watch?v=0G6d7TFVoy4