Why are some conflicts described as "external"? they are minor problems in a story. they pit a character against an outside force. they relate to events that happened in a character's past. they refer to political struggles taking place in a character's world.

An external conflict is a struggle that pits a character against an outside force, such as another character, or even nature. You can figure this out because external means that the source is outside the affected subject. So in this case the conflict is cause by a source outside the character.

All of the above would be correct.