The original Halo Wars was designed to be a standalone entry in the Halo franchise - no previous Master Chief knowledge required - and the sequel continues this trend. You shouldn't be worried about just diving in halfway through the story. That said, Halo has a vast and complicated lore/expanded universe which can be a barrier to new gamers - especially in the post-Bungie times that we live in. It's certainly no Dark Souls, but there is an awful lot to digest. With that in mind, we here at Kotaku UK decided it's worth putting together a primer for all the newbies out there. Gormless about grunts? Clueless about the Covenant? We gotcha fam.
Everything in this article before the picture of Master Chief on the beach has no spoilers from Halo Wars 2's campaign. I'll flag it up again at that point, but bear in mind everything after that picture details this new game's plot, so don't read that until you're ready. The rest of the text, however, has plenty of spoilers cherrypicked from all across the rest of the Halo canon, so you have been warned. Come on, it's a lore guide.
The Spirit of Fire
The last we saw of the Spirit of Fire was at the end of Halo Wars. The ship had sacrificed its slipspace engine to destroy a Forerunner shield world, preventing a serious Flood outbreak and ensuring the Covenant couldn't seize control of a fleet of Forerunner ships in the process. Without the ability to enter slipspace and travel at faster-than-light speeds, the ship was stranded decades away from UNSC-controlled space with the crew placed into cryogenic stasis until they were needed.
The first game took place in the year 2531, a mere six years after the Human-Covenant war began. Halo Wars 2 takes place in 2559 which is - deep breath, folks - 28 years after Halo Wars, six years after the end of the war in Halo 3, and about six months following the conclusion of Halo 5. Needless to say a lot has changed in the galaxy, though 28 years of icey stasis seems to have done wonders for Captain Cutter's complexion.
As far as we know, very little has happened to the ship in the years spent adrift. The short comic story Something Has Happened (featured in the Tales From Slipspace anthology) revealed that the ship's onboard AI Serina had been making repairs in the years following the first game. Unfortunately a Flood infection form had stowed away, infecting an engineer that had been woken from cryosleep in 2537. Over the next couple of days a minor infestation broke out, as the infected engineer woke other crew members from stasis in order to be infected. Eventually Serina enlisted the help of Dr Anders and Spartan Jerome-092 to quell the outbreak before she reached her seventh birthday. The trio were successful, leaving the ship and its crew to continue drifting.
Why the narrow time-frame you ask? Well seven years is the maximum life-span of a UNSC Smart AI. When they turn seven, AIs tend to go a bit loopy, and enter something known as rampancy. After seven years an AI's memory map becomes too interconnected, causing endless feedback loops that can't be reversed by human science. In simple terms they 'think' themselves to death. The state can occur sooner in AI that take on too much information (one of Cortana's fears following the destruction of the first Halo ring). The effects can also be countered to some degree, as seen in Cortana and Halo 5's Governor Sloan, but these actions are only very short-term solutions.
To counter the potentially devastating actions carried out by a batshit-crazy AI, the UNSC has a policy of terminating all smart AI at the seven year mark or the first stages of rampancy - whichever comes soonest. For this very reason, Serina deleted herself at the end of Something Has Happened, 22 years before the Spirit of Fire arrives at the Ark.
So far the UNSC has no idea what happened to the Spirit of Fire, leading it to be declared lost with all hands. It looked as though they came close to discovering the fate of the missing ship in March 2558 (Halo Escalation #5-6), but this ended up being an elaborate ruse by Insurrectionist forces.
The Banished are a new faction introduced in Halo Wars 2, but unlike Jul 'Mdama's reformed Covenant in Halo 4 they aren't one of the many post-war factions. Their origin begins long before the Prophet of Truth ordered the massacre of the Elites at the end of Halo 2 (an event known as the Great Schism, which kickstarted the Covenant Civil War). Anyone who has played Halo 2 will remember that the Covenant didn't react kindly to dissidence, or anything they viewed as heresy against their misguided religious fanaticism. Challenging the status quo, or speaking out against the Great Journey, was punishable by death.
The Banished is led by the Brute Atriox, who founded the movement after becoming disillusioned with the Covenant. His clan was routinely used on suicide missions, and after returning as the sole survivor from several missions Atriox decided he had had enough. He had seen his clansmen killed "39 at a time", and given his disbelief in the Covenant religion he saw no logic to needlessly warring with the humans. After finally refusing commands from Elite superiors, the Covenant leadership dispatched an assassination squad to end the perceived threat. Unfortunately for them, Atriox killed the would-be assassins and in the process inspired other rebels to join his cause. The year this happened isn't entirely clear.
The newly-formed Banished split from the Covenant, taking powerful technologies with them, operating as a mercenary group and waging war against the Covenant - forcing the powerful alien alliance to fight a war on two fronts. Following the Great Schism, that became three fronts, and you don't need to be a genius to see why the Covies couldn't cope. When the Covenant finally collapsed in 2553, The Banished were still a formidable force - which gave them a significant advantage over the other post-war factions that had to reorganise themselves from scratch. This meant they could reclaim even more technology and supplies, which proved useful when recruiting new members.
A very good example of this was how Atriox came to control the Covenant assault carrier Enduring Conviction. Following the fall of the Covenant, Shipmaster Let 'Volir had no desire to join the Arbiter's Swords of Sanghelios or Jul 'Mdama's reformed Covenant. Unfortunately going at things alone meant he had issues obtaining fuel and supplies, which is what drew the attention of Atriox and the Banished. 'Volir agreed to offer Atriox unquestioning loyalty in exchange for a constant stream of fuel and supplies, meaning the Brute warlord gained access to a powerful ship full of veteran warriors and equipment.
It's unclear how they came to be at the Ark.
The trailers have already revealed that Halo Wars 2 takes place on The Ark, a Forerunner installation first seen in Halo 3. It's best described as the central hub of the Halo array, and the name is very literal. It's one of two Arks built by the Forerunners, both of which were beyond the limits of the galaxy and thus out of range of the Halos' primary weapon.
The 'Greater' Ark was the birthplace of the original Halo Array (larger rings that proved too large to effectively implement), and was destroyed by the Flood in the waning days of its war with the Forerunners. The second 'Lesser' Ark, also known as Installation 00, that is seen in the modern era was created to build and maintain the smaller rings that we see in the games. Both installations were also designed to function as a refuge for Forerunners and other sentient species should the Halo rings ever be fired.
The Ark could be reached by conventional slipspace travel, though such a long journey would take many months. A much faster route was possible by travelling through the New Mombasa portal (as seen in Halo 3), which cut that journey down to a few weeks.
Following the aborted activation of Installation 05 in Halo 2, the entire Halo array went into standby mode. This meant everything could be remotely activated from the Ark's control room. An alliance between the Elites and the Humans (with some help from the Flood Gravemind) made sure that the Prophet of Truth was unable to do this. Following Truth's death, Master Chief and the Arbiter discovered the Ark had constructed a new Halo intended to replace the one destroyed during the first Halo game. They eventually fired this ring to put an end to the threat of the Flood, but because the ring wasn't fully ready, the firing mechanism destroyed the ring itself and caused serious damage to the Ark. Woops!
Roughly a year after the end of the War, the UNSC Rubicon was sent on a recon mission to the Ark to determine its status. The damage had caused serious problems with the installation's life support systems, and ground teams sent to investigate a mysterious signal on the surface had to suffer severe weather conditions and the threat of dangerous local wildlife. The signal eventually turned out to be the remnants of 343 Guilty Spark (previously thought destroyed by Master Chief), who proceeded to take over the ship in search of The Librarian. This left ground teams stranded, and having to fend for themselves. Only one soldier was able to survive, saved by the Ark's Monitor, 000 Tragic Solitude, for nefarious purposes.
Tragic Solitude (yeah, the Forerunners had some loopy naming conventions alright) had gone a bit mad over the years, and ditched the typical monitor body to upload itself directly into the Ark's systems. This meant it had greater control over the Ark than beforehand. Tragic Solitude was especially angry with the amount of collateral damage caused by the firing of the replacement Halo ring, and concocted a plan of revenge that would also let it retrieve the raw materials needed to make repairs. Since extensive damage meant the batshit AI was unable to open a slipspace portal from the Ark itself, it had to be rather devious about this.
In 2555 it used the captured soldier to kick-start a countdown of the Halo rings' firing mechanisms. The idea was that this would be discovered by the humans, who would reopen the Mombasa portal to try and stop the threat. Once the portal was open, Tragic Solitude would send through Sentinel Retrievers, who would strip-mine Earth and the rest of the solar system.
The plan was eventually ended thanks to a joint taskforce of Humans and Elites, a group that included Olympia Vale - the future Spartan and member of Jameson Locke's Fireteam Osiris. Tragic Solitude was destroyed, and the threat of the rings averted once more. Following this the UNSC began setting up scientific research posts across the Ark, and one of them would eventually become home to Isabel, the AI featured in Halo Wars 2.
We're about to get into spoiler territory now, so until you've finished the game you shouldn't scroll past this picture of Master Chief chilling on the beach.
As mentioned before Halo Wars 2 is a stand-alone title, so once you understand all the background there isn't really anything in the game's campaign that requires further explanation. A single Halo ring does play a large role in the plot, but since the crew of the Spirit of Fire missed all the fun towards the end of the Human/Covenant war they end up functioning as a proxy for all the newcomers in the audience. So nothing really needs explaining until the very end of the game.
Watching to the end of the game's credits nets us a cutscene typically reserved for the end of superhero movies. We see Anders' Halo ring drop out of slipspace unexpectedly, and coming face to face with a Forerunner Guardian.
If you haven't finished Halo 5, you should know that the Guardians are Forerunner constructs used to enforce the Mantle of Responsibility - which essentially amounted to the Forerunners telling the galaxy how to behave. Or else. The Guardians were activated before and during Halo 5, and it turned out a newly restored Cortana was responsible. Cortana was able to cure her rampancy using the Forerunner Domain and, by offering this discovery to other AIs, she founded The Created. Can't help but feel this one isn't going to end well.
Because they were now essentially immortal, The Created believed that the Forerunners intended for them, not humanity, to be the true reclaimers of the Mantle - since they have the lifespan and mental faculties to plan what was best for the galaxy in the long-term. The Guardians (and the Prometheans) were essential to this, since they would be able to enforce The Created's will and quell dissent.
It seems clear that the Guardian is the reason why the Halo dropped out of slipspace before it reached the planet Threshold. Why exactly isn't totally clear, but it's obvious that the Created wouldn't be happy with another Halo suddenly dropping into place unannounced. Since the ring is a clear replacement for ring(s) destroyed by Master Chief, it also means Cortana has the Activation Index on hand, and can potentially fire the ring without much effort. This makes it another tool for enforcing The Created's will, since the Halo rings' ultimate weapon can be adjusted so that the range is much smaller (as seen in Halo: Cryptum) - meaning it only affects specific planets or systems rather than the entire galaxy.
But that's speculation. All we know for now is that, despite having taken over the galaxy, failsafe measures had prevented the Created from accessing the Ark (mentioned in Halo Mythos)- which explains why they weren't present during Halo Wars 2. But now they have their own Halo ring, and the means to use it.