As the chapter (Chapter 7 of Book I) opens it’s been months, months of Arthur pulling the sword from the stone and the barons and the landed gentry and the knights all refusing to accept him. He keeps trying, though. Soon enough it’s Pentecost, which is part of the Movable Cycle so depending on the phases of the moon it’s anywhere from mid-May to late June. So literally five or six months of this. At Pentecost the largest collection of English aristocrats yet shows up, bringing along a bunch of knights and a huge mass of commoners, and once again, Arthur demonstrates that he can pull the sword from the stone and therefore is the rightful king. And once again, the barons and so on are all, nope, we don’t buy it, you’re way too poor-looking and scruffy and insufficiently powerful a warlord to be king.
But they miscalculated in bringing along an enormous pile of commoners, because the commoners are sick and tired of this back and forth, and accept Arthur as king (it’s no skin of their noses), and threaten to riot unless the barons come round. They’ll kill one thousand Arthur-rejecting barons a day for five days, they day, unless the barons swear fealty to Arthur. So the barons go ahead and submit, and apologize, and Arthur’s cool. He accepts their apologies and gets himself knighted/crowned by the Archbishop of Canterbury. There’s a big party.
This big party is sullied, sadly, by everybody and their dog coming to Arthur and complaining about how they’d been wronged by somebody else, and their nation had just gone to hell since Uther died, and what were their taxes paying for if not, et cetera, et cetera. Arthur listens to all of their complaints and clucks his tongue and says he’ll see what he can do. A lot of barons whose estates had gotten very large since Uther’s death discover that Arthur is a redistributionist, as he seizes parts of their lands and turns around and gives it to the various impoverished gentry whose land it had been up until somebody seized it. They’re cool with this, the rich barons are, on account of they don’t want to get lynched.
Anyway, Arthur sets up rebuilding some kind of government, and puts Kay and the other knights who have stuck by him all spring during Sword-in-the-Stonegate, he puts them in charge of various things, and he sets about conquering all of the island of Great Britain that he doesn’t already rule — everything north of the river Trent, including Scotland, and most of Wales. This takes a while but after a year, maybe two, it’s all done with. That’s what Malory says here, anyway; he’s about to super contradict himself about it. So let’s assume he’s more consolidating his power in the greater London metropolitan area, with the fat-cat land barons and the angry peasants and so on. It sounds like something that would take a while to work out.
Arthur hasn’t done much at this point, really, but already I like him about ten thousand times as much as Uther: he’s humble, he forgives his enemies, he seizes the ill-gotten gains of the wealthy and returns them to the poor (albeit the poor nobility rather than the poor in general). Here’s hoping he doesn’t get Merlin to help him rape anyone. Also, I can’t help but notice that according to Malory, Arthur and Merlin haven’t met yet. When I was a kid I watched Disney’s Sword in the Stone a bunch, and as a teen I read the first half of Once and Future King multiple times in unsuccessful attempts to make it through the whole thing, and one thing I do remember is that Merlin and Arthur had a Doc Brown & Marty McFly relationship, in that version of the story. Plus, lots of shapeshifting, which hasn’t come up yet in this version of the story. So that’s kind of an interesting change. Merlin himself comes across as much more Gandalf the Gray than I was expecting, too; he’s all the time setting events into motion and telling kings what to do.