One common external conflict situation in novels is character vs. nature. For example, in 'The Old Man and the Sea', the old man has to battle the powerful sea and the big fish. Another is character vs. society, like in '1984' where the protagonist struggles against the totalitarian society. Also, character vs. character, as seen in 'Romeo and Juliet' where the two lovers face opposition from their feuding families.
External conflict situations can enhance a novel's plot by creating tension. For example, in a character - vs - nature conflict, the constant threat of a natural disaster keeps the reader on edge. It also drives character development. When a character faces society's norms (character vs. society), they have to adapt or fight, which reveals their true nature.
Basically, an external conflict occurs when a character has to deal with something outside of themselves that opposes their goals or desires. It could be a physical obstacle, a person with opposing interests, or an environment that's hostile. These conflicts drive the plot and force the character to take action and grow.
External conflict often involves rivals. In many romance novels, there's a third character who is also interested in one of the protagonists. This rival can create a lot of tension. They might try to break up the main couple by spreading rumors or causing misunderstandings. Also, environmental factors can be a source of external conflict. A natural disaster or a difficult living situation, like poverty or living in a war - torn area, can put stress on the relationship and force the couple to face challenges outside of their feelings for each other.
Maybe it's the conflict between two powerful factions vying for control. This type of external conflict can introduce intense drama and shape the course of the story.