If you've been following Valve leaks at all over the past few years, you'll know the story of Deadlock. For the unaware, it first leaked under the name Citadel, a clear reference to the towering Combine structure in Half-Life 2. It then changed to Neon Prime and later Shadowline before becoming the Deadlock we know, dropping its ties to the Half-Life and Portal universe completely.
According to Valve leaker Gabe Follower (and as reported by Dot Esports), the game would've been set during the Seven Hour War in which the "Combine fought against the rebels of the streets of City 17." While not clear cut evidence, much of the architecture in the Deadlock you can play right now looks strikingly like that of City 17, so it certainly lines up.
If you need to brush up on your Half-Life lore, here's a quick recap; the Black Mesa Incident in the first game opened a dimensional rift that allowed aliens from the borderworld Xen, led by the Nihilanth, to invade the facility. While Gordon Freeman was in stasis, an interdimensional empire known as the Combine learned of Earth through that same rift.
While they have the ability to...