Internal conflicts occur within the character's own mind. For example, wrestling with a moral decision or facing fear are kinds of internal dilemmas a character might experience. External conflicts are often categorized as man vs. man, man vs. nature, man vs. supernatural, man vs. technology, and man vs. society.
Ray Bradbury wrote "A Sound of Thunder" in 1952. The setting is 2055, and the premise of the story is that a man named Eckels is going back in time to hunt a Tyrannosaurus Rex. One of the external conflicts is man vs. nature, which specifically is the hunting of the dinosaur.
"Some dinosaurs have two brains, one in the head, another far down the spinal column. We stay away from those. That's stretching luck. Put your first two shots into the eyes, if you can, blind them, and go back into the brain."
Another external conflict occurs as a man vs. man conflict between Eckels, the protagonist, and Travis, the safari guide. Eckels is shocked at the sight of the dinosaur and doesn't have the courage to take a shot. In his fear, he compromises the entire mission. He is told to return to the time machine, and in doing so, he steps off the path. Travis wants to leave him in the past for this egregious error.
"'Get up!' cried Travis. Eckels got up. 'Go out on that path alone,' said Travis. 'You're not coming back in the Machine. We're leaving you here!'"
A third external conflict is man vs. society. Travis explains that the government doesn't want them conducting time travel expeditions because the consequences are too grave. If anything is disturbed in the past, it can create ripples that change history in inconceivable ways. In order to operate, the company has to pay the government "big graft" (bribes). Travis tells Lesperance the consequences of Eckels's carelessness:
"This fool nearly killed us! But it isn't that so much, no. It's his shoes. Look at them! He ran off the Path. That ruins us! We'll forfeit! Thousands of dollars of insurance! We guarantee no one leaves the path. He left it. Oh the fool! I'll have to report it to the government! They might revoke our license. Who knows what he's done to time, to history!"
After Eckels begs them not to leave him and the group returns to the present day, they find that society has indeed suffered as a result of Eckels's actions. Instead of Keith being president, a tyrant holds the office. All of society has been affected negatively by Eckels's failure to follow the rules and the warnings.