In the penultimate episode of Game of Thrones Season Six, "The Battle of the Bastards," the Starks finally found their way into a win. Though the fight against Ramsay looked entirely hopeless, the cavalry arrived at the last minute to secure their victory: thanks to Sansa sneakily asking for help from Littlefinger, the Knights of the Vale saved the day. Ramsay was justifiably turned into dog chow and Winterfell flew Stark banners once more. Still, this doesn't mean the trouble is over – far from it. In the trailer for the finale, "The Winds of Winter," Jon tells Sansa that they have to trust each other because they have so many enemies now. But who are Jon and Sansa's enemies?
Thankfully there are no Boltons left to torment the Starks any longer, but other dangerous forces remain. On Game of Thrones, a threat will arrive just in time to take the place of a recently demolished villain – just as Joffrey was traded in for Ramsay, someone else will step up to take the Boltons' place. There are all the Northern Houses that either supported Ramsay or refused to support Jon and Sansa: the Umbers, the Karstarks, the Glovers. Not to mention old enemies like the Lannisters and newer enemies like Daenerys (maybe Theon can put in a good word for his old pals?). It's also possible that Littlefinger, the ultimate wildcard, could shift from friend to foe.
The Other Houses
Despite Sansa's insistence that the North would rally around them, it turned out to not be the case. It was understandable (mostly), from the side of the Northern lords: Jon and Sansa looked like they were fighting a losing battle, and everyone was still recovering from the last time a Stark declared war (R.I.P. Robb). However, now that the Starks have come out on top again, that puts the rest of the North in a precarious position. Do they pretend they were never Team Ramsay and swear fealty to the Starks? Do they try and oust the Starks once again and take over? It could go either way, especially because Jon and Sansa's position is far from secure.
The bad blood between the Lannisters and the Starks goes deep and that hasn't changed with time. The Lannisters are responsible for the deaths of Ned, Catelyn, and Robb, as well as Sansa's torture at Joffrey's hands and her marriage to Tyrion (p.s. is that still valid or nah?). The Starks will present a threat if they ever manage to rally the North and turn them against the Crown. Even with Jaime being a secret Tully fanboy, it doesn't look like relations will improve between the two families any time soon.
As the Lannisters' partners in crime, the Freys also present a problem. They're probably too busy with Riverrun to worry about Winterfell just yet, but they will still be an issue that needs to be dealt with.
Dany may not be a major player in Westeros yet, but with her brand new ships it looks like Dany could be crossing the sea any day now (finally!). Her attempts to conquer could ruin things for the recently re-installed Starks – unless they decide to partner up, of course. That could always be the case, especially if Jon's family lineage does end up connecting him more closely to Dany.
Littlefinger has taken an unfortunate shine to Sansa and he's sure to be looking for repayment after lending her his army – no matter that he owes her that and more for hitching her to Ramsay in the first place. The promo for the finale shows Littlefinger in prime creeper mode: when Sansa asks what he wants, he tells her that he "thought she knew what [he] wanted," which fans have interpreted as a potential marriage proposal. If Sansa says yes, this could give Littlefinger control of the North, which I can't imagine anyone but him wants as an outcome; if she says no, she could be adding another name to the enemies list.
The White Walkers
The Walkers are really everyone's enemy, but they sure do have a soft spot for Jon and they're definitely planning some major trouble down the line. It's not a matter of if the conflict arises, it's a matter of when. They're coming at some point but hopefully their arrival isn't imminent; I don't think poor Jon Snow could handle another battle right about now.
Jon wasn't exaggerating when he said they have a lot of enemies and this is Game of Thrones, so you have to be prepared for anything. With a list longer than Arya's kill list to keep an eye on and a very tentative hold on the North, things could turn south again for the Starks soon – but fingers crossed it's not too soon.