The episode is a sort of a follow-up to the fifth season episode "I, Borg". For those unacquainted with "Star Trek", Borg are the chief antagonists of the Federation in this series. They are automated cybernetic organisms, connected into the Borg Collective. They have no individuality and their sole purpose is to assimilate other species and races into their Collective. In "I, Borg", the crew of the "Enterprise" captures one of the Borg who influenced by them develops individuality. This Borg, named Hugh, was later returned to the Collective in hope that his sense of individuality will spread around it thus causing the Borg race to be changed forever.
In "Descent" we see that the plan to infect the Borg with individuality worked but the results were far from those expected. The infected Borg were severed from the Collective, and among the outcasts began to reign chaos. Since they had no previous sense of individuality the cast-away Borg had no idea what to do with it, what kind of community to create, or give themselves a purpose for their existence.
As such, they became prey of Lore, the evil twin of the android officer of the "Enterprise", Lt.Commander Data. As Hugh, whom we meet again in this episode, recounted, it was not hard for Lore to seize power over the Borg:
"...we had no idea even how to operate our vessel. When Lore came we were ready to listen to anyone that had promised change and a way out of this situation. We all gladly followed at first his promises of a glorious future. When it became clear he had no idea how to fullfill these promises, he began talking of sacrifice..."
Lore had managed to find a purpose and meaning to the cast-away Borg. Instead of assimilating species like they used to do, the new Borg, which became more agressive and skillful, began destroying them. In short, the new Borg became a more deadly and vicious enemy then the old Borg ever were.
I believe you already recognized some similar situations from human history. Traditional society torn apart, disorianted population, unaware of it's role in the world and in history, brought to the point when they are ready to follow anyone that promises redemption. But this episode is more then a simple warning against false messiahs...
This episode is propably the best argument in favour of the so-called "prime directive" and the principle of non-interfierence into traditional societies of other nations and cultures, even those hostile to our own. As one could see, even if one manages to initiate changes within the enemy it is by no means a guarantee that this change will be for the better. And we need not go too far in tha past to confirm it. All that it takes is to see in whose hands Iraq ended up after Saddam Hussein was deposed.
Contemporary generations in the west, even the elite, are more versed into pop-culture then in classical sciences. Unfortunately, most have picked wrong films and series to shape their worldview. This is why we are in such a sorry state...