Yes, it is basically how it worked. Zones were locked by victory points or by timer (Keep timers 2 hours (in T4) when captured, BOs 30 mins). The timer system was changed a few times. In the begining the timers would start with a capture, but later it was changed (Keep only) so a guild had to claim the keep for the timer to start. The BOs was also changed from being open for capture at all times to open when the timer was under 15 mins (Can't remeber if it was 15 mins). Victory points was gained from different aspects of the game. Controlling BOs and Keeps, killing players in RVR, Scenarios, PQs, Victory Points from lower tier (based on the standing in the tier beneath, standing in T3 if we are in T4).
The way you got to the city was also changed. If dest as an example captured Praag and then Reikland, the order fortress (Reikwald) would be open for capture. It was build like a big Keep with a Keep lord and worked like a PQ. The PQ timer would start with the capture of Reikland in this example (I can't remember how much time).
If the attacking faction succesfully kills the Fortress lord in time, they win (Loot bags like PQs) and the main zone will be locked for 3 hours (I think).
If two main Zones are locked at the same time, the city will be open for invasion.
The city instance also changed a few times. In the begining invaders objective was to kill x amount of defenders (mobs spawned in the city and counted as defenders), destroying objects. The defenders objective was to kill invaders, repair objects. It's a race to complete the tasks and whoever does it first wins. Whoever wins, decides who will get a shot at the Invader gear PQ (Kill Adell The Corrupter if order and can't remember dest PQ). If the PQ is done in time a reset timer will begin and bags rewarded etc. After the reset timer hits 0, we start all over with the first part again.
http://www.youtube.com/watch?v=UXrQFQJBOG4 - Stage 1 (Kill players)
http://www.youtube.com/watch?v=KyFwg_TcJUE - Invader PQ Order (Adell The Corrupter)
Later they changed it to Battle Objectives (Capture = like in Scenarios). The Objectives generated points. The first to get 500 would win. Invader PQ would start for the winning faction.
A city could be captured by Victory Points, Victory Points was gained by winning in the instance. The total victory points was not from one instance but all instances together, so it was a team effort to lock the city.
This is a long time ago so a lot of this might be inaccurate, so everyone please make corrections and add.