While the first two entries in the Borderlands series did focus on lore and world-building, the following two chapters did a much better job at expanding the universe beyond Pandora. Starting with Borderlands: The Pre-Sequel, which reveals the story of how Jack became the villain he is in Borderlands 2 and also features a mysterious Guardian called The Watcher, Gearbox started planting the seeds for the events of future games. In Borderlands: The Pre-Sequel, players have to stop Tungsteena Zarpedon from destroying Elpis, the moon of Pandora, which she tries to do in order to stop Jack from opening the planet's Vault.
However, the events of Borderlands 3 and the lore from Borderlands: The Pre-Sequel make it clear that Zarpedon was only trying to stop the chain of events that would lead to Elpis being used as the key to open the Great Vault - Pandora itself - and unleash the Destroyer. This knowledge that the commander had acquired came from the Vault on Elpis, where she and her team found The Watcher, who opened the Vault and led them to its treasure: knowledge of what could be. The Watcher is a key figure in Borderlands: The Pre-Sequel, and even saves Athena from a firing squad about to kill her under the command of Lilith, only to warn the astonished bystanders that they would need every Vault Hunter they could get for an impending war.
Why Borderlands 4 Should and Shouldn't Address The Watcher's War
The Watcher's war was never truly explained nor touched upon again after the events of Borderlands: The Pre-Sequel, and it seems like Gearbox wants to expand the universe of the Borderlands series more before delving into it. This is precisely what Borderlands 3 did, as it was the richest installment of the saga in terms of lore, and especially so thanks to the Eridian Writings left by Nyriad - an incredibly powerful Siren who lived long ago. Nyriad's writings explain how the Eridians met their end, as it was her who killed them, not out of thirst for blood, but rather because it was their wish to be consumed by the Leech in order to power up the Great Vault and contain The Destroyer within it.
This intricate series of events is likely connected in a way to the war foreseen by The Watcher, but given it has been a long time since it was last mentioned, this poses the question as to when this conflict will spark. A likely candidate comes in the form of Borderlands 4, considering that all the games in the series thus far have built up to something bigger and greater than a bunch of Vault Hunters. Still, there are pros and cons to Borderlands 4 being the game where the war finally occurs.
The war predicted by The Watcher seems like the biggest event to ever happen in the Borderlands universe thus far, and as such, it should be a natural and unavoidable step that moves the story of the whole franchise in a very specific direction. It shouldn't just be something that Gearbox throws at its players as the inciting incident for the events of a new game, but rather the war should be the culmination of an entirely new chapter. This huge conflict could spark towards the end of Borderlands 4, rather than at the very beginning of it, especially because Tiny Tina's Wonderlands is likely not going to address touch much on the topic - if it all.
And yet, without further mentions of it, The Watcher's war poses the risk of being forgotten about, becoming a less relevant event if it's not addressed in other games of the series. It's hard to strike a balance with this sort of thing, but Borderlands 4 should either straight-up handle the war, or maybe explore the root causes of this conflict and build its narrative from there, leaving it up to yet another game to tell that story in full.
Borderlands 4 is rumored to be in development.