Javier (Pibe) said:
Personally, gangs are necessary to call someone's attention for: his lack of diplomacy, his imperialism, his lack of rationalism, abuses, etc.
I don't agree with this. Nations will often gang a nation despite the amount of diplomacy he engages in, how much care he cares to make sure he isn't considered a major threat etc.
Taking one of my experiences.... In NO4 I was Denmark, not particularly expansionist (I had a couple of german provinces and baltic provinces). I did diplomacy every week with every nation except Austria and OE (in a game of 12+ players, no minor feat

), I was constantly ganged by an England with great leaders, Brandenburg, an oppurtunistic Holland (and at times Sweden, Portugal, France, and Spain). Every session I could expect at lest 1 or 2 of these wars, with the only reason being that I had a trade empire and scattered colonies and had tried to be a colonial power.
Despite my best efforts, I was always the punching bag of europe, even though I was never close to being the strongest nation or having half decent leaders. I continued to be the punching bag since the nations doing it were never at war with each other or had any fears for their security, so they were free to make my experience as frustrating as possible. After a couple of years of this I simply had to stop playing because it had gotten ridiculous (I had to be subbed so England, Portugal (who was my ally!), Holland etc all ganged my sub).
It's gameplay like this that makes a game not fun, and makes people lose interest in MP altogether as I did. I have nothing against a reasonable gang if a nation gets too strong, as long as it's not oppurtunistic and repetitive. In Realpolitik diplomacy gangs aren't too much of a worry, because diplomacy is fluid. But let's face it, the problem is that often that nations are left to bully certain nations, safe in the knowledge that no one else is going to touch them.
It's not a failure of the gangee's diplomacy or gameplay, it is failure of bystanders A. to allow the gangee to get to the size where he needs to be ganged or B. to allow the ganger to grow more powerful at expense of the gangee.