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The similarities: the way contribution is calculated and the fact that they are "events". RIFT is a descendent of WAR, but GW2 is from a different family altogether.
RIFT and Warhammer's events are built in "Stages" while GW2's is based on "Chains". While all dynamic events in all MMO's share the definition, GW2's did not evolve from WAR/RIFT's. It's more of a parellel evolution, per se and not a direct descendent.
1. In Warhammer they are permanently located on the map on a small parcel of space. They run in a cycle that is clearly visible in the UI with a countdown timer that clearly shows what stage a player is on. At the end of the event, contribution is weighed and a random lottery decides who gets loot and who doesnt'. These events do not scale based on a player level, so higher level players can make quick work of them, regardless of how epic they were to lower levels.
2. In RIFT (made my several ex Warhammer Devs) they took this sytem 'up a notch' by making the events more interactive. They can be spawned by players and don't show up on the map until spawned (or ready to spawn). RIFTS have multple stages that are clearly shown on the UI that help a plaeyer know of it's progress. Once a RIFT is complete, it disappears and everybody is rewarded based on contribution. Another wrinkle that RIFT brings is "zone events" (which I haven't seen any other game do as smoothly) where an invasion force roams the countryside. They are mobile and can be dangerous. Again, events in lower level zones can be handled quite easily by higher level players.
3. In GW2 events are "chains" that are spawned by any number of ways and can travel great distances across the map. The only UI indication a player has is the progress in that particular part of the chain. If one part of the chain fails, the story usually takes a different turn which will can involve any number of different other events that are available. With the exception of a zone wide dynamic event, there is no indication of an event until a player stumbles upon it. They can be spawned by killing a certain mob, picking up an item, talking to an NPC, opening a cage door, or just overhearing a conversation. Some chains are very short, while others are extremely long and involved. In my experince most people run away to do other things after completing a link in the chain, not realizing they missed the best part coming up. XP, Karma and coin are given based on contribution and occasional a "chest" will spawn on particularly large zone events. Players level will scale to the level of the event, so while higher level players are more powerful, they are never trivialized.
To summarize: WAR and RIFT events (not invasions - those are unique!) are small events that occur in visible stages while GW2 events are CHAINS that will often branch in multple directions. They are all "dynamic events" by definition, but to say that GW2 is a evolution of the WAR/RIFT model would be incorrect since they are so different. So, to say that GW2 somehow evolved from WAR or RIFT is incorrect. GW2 evolved parellell to them, and is not a descendent of them.
If in 1982 we played with the current mentality, we would have burned down all the pac man games since the red ghost was clearly OP. Instead we just got better at the game.