
Indiscriminate slaughter of unarmed humans attempting to escape City 17 or help others do so? Check. A literal "beating quota" for Civil Protection officers? Check. Ruthless lobotomization and forced cybernetic augmentation to their army of transhuman slave soldiers? Check. Using headcrabs as biological weapons to inflict a horrifying fate on anyone who gets overtaken by one? Check. Aliens Are Bastards: Oh boy, where to start? Completely unprovoked and imperialistic conquest of an entire species (one of millions no less)? Check.Airstrip One: The remaining cities under their control on Earth are simply given soulless numerical designations, with Half-Life 2 and its episodes being set in "City 17," located somewhere in Eastern Europe.In short, despite their vast, galaxy-conquering might, the Combine regime is bloated and inefficient, at least on a planetary scale, and Earth's Resistance is like a parasite taking down a much larger host that's simply so big it can't concentrate its power properly to destroy it.Unfortunately for them, the destruction of the City 17 Citadel and the closing of the Superportal above its ruins means that the remaining Combine forces on Earth are stranded with no backup, and considering the City 17 Citadel also doubled as their only way to communicate with their off-world command center, it's safe to say that humanity actually has a fighting chance against the Combine forces still remaining on Earth. However, if they could harvest that portal technology they would be able to move their forces around the universe in a blink of an eye, making them effectively unstoppable. The Combine have no such technology and must slowly drive their fleets across the universe in real-time, which makes long distance travel too much of a resource dump to actually justify doing.

Once the Citadel blows up, it's revealed the reason they're so interested in Earth is that we discovered true long-distance teleportation technology at both Black Mesa and Aperture Science. Thus, the Combine forces on Earth are cut off from the main bulk of the empire's military forces and it is only through the Citadel that they are able to maintain a decently sized militia.

At the same time, much like the real-life Roman Empire, their massive size causes all sorts of bureaucratic kerfuffles and makes actually mobilizing that immense power difficult to say the least. They have advanced technology, competent tactical ability, ruthless efficiency, and a track record for not being trifled with. Achilles' Heel: The Combine are an impossibly vast inter-stellar and possibly trans-dimensional empire of massive size and scope.And that's to say nothing of the people actively being oppressed by them. Even the people who are actively employed by it such as Doctor Breen or the collaborator scientist in Alyx seem at best contemptuous of it or dislike the organization itself (Breen himself calls them "the Combine" despite treating this name as almost an insult in one of his broadcasts). 0% Approval Rating: Absolutely nobody likes the Combine.Think a far more overtly villainous Imperium of Man mixed with the Borg Collective.

Their occupation force on Earth, the Overwatch, consists of a portion of their transhuman forces (modified humans using human vehicles and weapons) and "Synths", aliens who have been modified and outfitted with cyborg attachments and pulse weaponry. A powerful trans-dimensional alien empire, they conquered the Earth and are the main antagonists of Half-Life 2 and its Episodes, as well as Half-Life: Alyx.
