For example, my current setting I started with a couple ideas:
there's an island with five regions, there used to be a sixth. Something happened and it was annexed.
The two larger regions are about to go to war, but aren't right now for some reason. Something the players will do will remove the reason and start the war.
The lord of some region disappeared 20 years ago. Is he dead? Is he just missing? Where is he? I don't know yet. I do know he outlawed a sect of the major religion. Idk why
The major religious center is gonna be overrun with goblins at some point. Idk why yet. It has something to do with a sorcerer collecting bodies. Idk why he wants the bodies.
The sorcerer also gives out coins for corpses he collects. The coins cause the holder to dream the happiest memories of the person before they died.
I basically pulled this stuff out of my ass or ripped it from stuff I like. Or decided it out of convenience for what I had prepared. Then the players did some stuff and I had to come up with some answers.
After speaking a specific ancient chant, the coins are "traded" (to whom idk) and a demon is summoned as a thrall for the chanter for a short while in combat. So the sorcerer has some affiliation with demons.
The party cleared a cult out of a fortress on the border between two big regions. The region was "cursed" and that was preventing the armies from moving against eachother. Now it's clear. War is certain.
I decided the religion was a Berserk like thing with the godhand serving Tiamat and the religion mistakenly believing them to be good. All the saints in the area are actually named after former demon lords under Tiamat. The local lord's buddy betrayed him to rise as one of the godhand (like angels, above the popes) and so the lord destroyed all the temples celebrating saints associated with that sect of the religion and he left on a quest to find and kill his friend the betrayer.
Now the setting is filling out already. But because I was forced to answer questions about the bigger picture to fit the smaller picture, it feels more organic to me. It feels like it has varying level of detail and question unanswered, like reality, rather than a homogenous number of layers of depth that I've gotten from top-down approaches in the past