Danny, you had one job to do. Just one job. I knew his return to the hidden city of K'un-Lun was going to come with a few hold-ups (nothing is ever easy in the Marvel universe), but things are much, much worse than that. So what happened to K'un-Lun on Iron Fist? That remains unclear for the time being, but one thing's for sure — Danny's home is in some serious danger. Warning: spoilers from Season 1 ahead!
After defeating Harold and finally coming to terms with his parents' deaths, Danny decided that the best thing to do would be to return to the city he grew up in and complete his training. He also asked Colleen to come along with him. But when they arrived, all they found were streaks of blood, a few dead fighters, and an empty space where the city used to be. So who exactly attacked this place and where did it disappear to? That's something viewers probably won't find out about when/if the series gets picked up for a second season. However, if I had to wager a guess, I'd say it would make sense for Bakuto, the leader of The Hand, to be behind it. Though where he would've taken it, I can only imagine.
While it seemed as though Colleen had defeated Bakuto during their little Central Park showdown, his body quickly disappeared soon after, making many believe he may have shared Harold's ability to come back from the dead. It makes sense Bakuto would've treated himself to this advantage. And since no one thought to behead him, it's very possible he's still at large.
Based on everything he shared with Danny upon meeting him, he's become somewhat obsessed with the legend of the Iron Fist for quite some time now. So it would make sense that he'd want to track down the place that helped Danny become the superhero he is now. And considering he knew that Danny was a little too preoccupied with his own life in New York City, now would've been the most opportune time to attack. Davos warned Danny that with him gone, no one was there to protect K'un-Lun's boarders, leaving the city unprotected. It appears as though his fears have now come to pass.
Granted, maybe Bakuto isn't behind this and it'll end up being a new Big Bad fans will get introduced to later on. But from where I'm standing, Bakuto is our most likely suspect. But as for what his next move will be (also, how does one go about moving a city?), that's something we'll have to find out about at a later date.