I’ve always wanted to know where the combine came from, Ever sence I played Half-Life 2 there has been two questions lurking in my mind: “Where did the combine come from?” and "What the hell happened between HL1 and HL2.
I know about the 7 Hour war and Earth’s surrender but nothing else. I just can’t find info on it.
The legend goes that The Combine were attracted to the portal storms, pushed into our universe, and decided to take over earth because, well, it’s what they do. But it’s also implied that Breen was aware of the Combine, and contacted them prior to the resonance cascade, with the promise of power. if you wanna know what more or less happened between HL1 and the combine invasion, see The Mist.
Everything else is either a mystery, or completely obvious.
P.S. Also, you could have just googled it.
I thought they came from a different dimension 
There is also a mod that fills the gap between the 2 games.
Check it out at https://operationlambda.com/
[COLOR=‘Black’]/shameless plug
:3
I thought Breen contacted them towards the end of the Seven Hour War and negotiated the surrender, rather than before the Resonance Cascade.
^^ That’s what I always figured to be honest.
I thought Mist was an influence rather than a HL plot component?
no shit?
The OP asked about the plot of the HL universe, specifically what happened after BM and before Gordon woke. Mist really does not answer any questions regarding HL.
Besides the 7 hour war and earth’s surrender, I think everything else is left to speculation until Valve fills in the blanks.
I’m just drawing from my hard copy of HL2: Raising the Bar, here.
If you took my comment literally, well shucks pardner, whut kin’ ah say
Yea sorry I took it literally. Thought that perhaps the official HL canon actually referenced events in mist and that I was out of the loop…again.
maybe the xen aliens brought technology to earth to modify humans to combines or just to create them and breen just used this technology for his interests to take over earth?
Get your facts straight son.
@ MechUnit then how do you explain the GIANT FLYING MAGGOTS WITH PSYCHIC POWERS BRAIN-SUCKING TONGUES AND ROBOT ARMS
Well in Half-life 1 you “Close” a portal, however the Combine manage to open this portal again and being able to invade Earth, the earth is being toke over in just 7 hours because Dr. Breen (administrator of Black Mesa) manages earth’s surrender. this is why the combine rewarded him with power.
The combine are forcing everyone to get high as fuck?
Sorry…obviously just a spelling mistake, still made me laugh…
“Do you care if the Combine empire falls?”
“Fuck it.”
That’s how they won the war. No one felt like fighting back. 
Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.