Instead of a villain or an internal conflict our story’s antagonistic force could be the circumstances in which they find themselves. The job they hate has no malice against them and isn’t a person but it creates conflict. Finding themselves in a hostile environment doesn’t mean there’s a person that caused it but they still need to survive it, another conflict. When a protagonist is transported to another world there might be villains within that world but there’s also the problem of how to get home to overcome.
There’s more than one type of serious circumstance. There’s the type of circumstance they’re put into by a person or collection of people (The Hunger Games), the trials they go through to defeat a villain (Lord of The Rings), or there’s the circumstance they find themselves in that contains villains but they weren’t put there by a villain (Alice in Wonderland or The Wizard of Oz). These circumstances don’t have to be hostile environments like the arena in The Hunger Games or The Mines in Lord of The Rings, but they have to feel hostile to the protagonist such as an office. There’s nothing innately hostile about an office as a setting, the people might be hostile, the job might be boring, the commute might be a nightmare but it’s unlikely the protagonist will be squashed by a boulder or fall into a pit of snakes. The antagonistic force of a place doesn’t have to mean physical danger.
Another antagonistic circumstance we may have in an office in the fight for promotion. If two characters have a chance at promotion it doesn’t have to mean one of them is a villain. The circumstances are competitive but this doesn’t have to mean characters dislike each other, it can actually increase the conflict if the two characters like each other because they want to win but they don’t want the other person to lose. The people involved in the situation aren’t antagonists, although they might begin to behave like it due to circumstances, it’s the circumstance that creates conflict therefore the circumstances are an antagonistic force. If these two characters hadn’t been put in these circumstances would they have become antagonists? If not than your antagonistic force is probably the circumstances themselves.
In The Wizard of Oz Dorothy defeats The Wicked Witch of the West but she originally sets off to meet The Wizard to find a way home. The circumstances bring her into conflict with The Wicked Witch of the West. Once The Wicked Witch is defeated Dorothy still has to find a way home, her primary conflict is unresolved by defeating The Wicked Witch, the circumstances are still creating conflict.
Whereas in The Hunger Games once Katniss has survived the games President Snow still has to be defeated. In Lord of the Rings the Fellowship travel through various dangerous circumstances and each one takes them closer to defeating Sauron, the antagonist of the story, the goal is to defeat evil and this isn’t achieved solely by defeating an orc army or crossing Mordor. Once Frodo and Sam cross Mordor they still have to throw the ring into Mount Doom to defeat Sauron, evil manifested. In these cases surviving a situation doesn’t resolve the overall problem.
At the end of The Lord of the Rings the characters still have to return home but this is a secondary conflict. The primary conflict was ‘How do we defeat Sauron?’ and the return home is ‘Now we’ve defeated Sauron how do we get home?’ it’s a new conflict, albeit an inevitable one because they travelled so far to conclude their primary goal.