A meme I've seen growing in popularity, especially in the past year with the rise of the HBC, is the idea that coalitions and powerblocs are a new thing. "Back in the day," the game was more fragmented, smaller groups had a chance, so on and so forth.
The idea that coalitions are a "new thing" is just plain wrong. EVE's first Great War featured a coalition that included (among others) Reikoku, Black Nova Corporation and Evolution waging war on Phoenix Alliance and its myriad allies. Prior to the destruction of Phoenix Alliance in this war, its leadership dreamed of a "super alliance" of alliances. This idea lived on much later in the form of the many iterations of the Northern Coalition - for newer players, that's not to be confused with "Northern Coalition."
RedSwarm Federation was formed in late 2006, a pact between Goonswarm, Tau Ceti Federation and Red Alliance to make war on the Southern Coalition, comprised primarily of Lotka Volterra, Veritas Immortalis and Knights of the Southerncross. After BoB terminated the rotting heap of garbage known as ASCN, they installed vast swathes of pets/renters/vassal alliances, which was a coalition of sorts and planted the maddeningly wrong idea in people's minds that persists to this day that all coalitions function on a pet/master relationship. In short, examples of coalitions exist throughout EVE's history.
And yet, the meme has some elements of truth. Both the old Northern and Southern Coalitions had membership in excess of ten thousand. Undeniably smaller than either the HBC or the CFC, they would nonetheless be some of the largest groups in the game if they existed today, and at least on paper, would not be tackled lightly. Nevertheless, the forces deployed by the coalitions of today are powerful beyond anything players of that age could have dreamed of.
So what changed? And in particular, what has changed in just the past year or so, recently enough to have given the impression of "newness" to the concept of a coalition?
Most of it, I think, exists in the metagame. For example, while some of us respect it far more than others, both the CFC and the HBC have a tightly integrated IT apparatus, which they encourage coalition members to register for and use. That, in turn, helps to facilitate an extremely high degree of coordination. Combined ops become easier to manage, coalition-wide fleet doctrines become easier to propogate and enforce, et cetera. Perhaps even more importantly, it encourages a higher degree of bonding between corps and alliances. When times are good, that's no big deal, but when adversity strikes, those bonds can be the difference between weathering the storm and sinking like a stone.
Likewise, the composition of modern coalitions has changed. The Northern and Southern Coalition were huge, as was the old mega-alliance ASCN, but they were also bloated with carebears. Pure carebears, that is, the sort that existed only to build things, or mine, who had never shot another player in their lives. Darwinian predadation by more militant groups has almost entirely purged those sorts of entities from nullsec. Self-described industrial corporations or alliances continue to exist, of course, but when push comes to shove, they pick up their guns and fight alongside their allies in "pure PvP" organizations. Consequently, a modern coalition tends to be far more potent than many such older examples, regardless of actual size.
And finally, if there is one factor that has led to the growth of super-coalitions, it would have to be the servers themselves. Many players look back fondly of the good old days, but only through thick rose-tinted glasses. In those days, the servers would start to creak in engagements between even just a few hundred players, and more than one fight for a system was won or lost by who could log back in faster after the node crashed under the weight of a thousand players. I suppose it might have felt like "good fights" were had if you were the one being jumped into... who doesn't enjoy a turkey shoot, nuking players who are locked up and helpless? More often than not, anything CCP tried to make things better failed, even when it "succeeded." Always eager to push things to the limits, players simply threw more pilots into fights.
All that changed a year ago with the deployment of Time Dilation. Overnight, 1200 player battles went from node-crashers to no big deal. Hundreds of goons descending upon Jita and blowing up everything they could during Burn Jita gave an example of what is possible. And as before, when allowed to bring more players, more players are brought, because whether you like or not, EVE is and probably always will be a numbers game.