An event, revelation, or a new character that creates a problem the protagonist must overcome is called the
conflict
exposition
plot
theme

An event, revelation, or a new character that creates a problem the protagonist must overcome is called the conflict. In a story composition conflict is the turning point of event, when a challenge is met by the protagonist. The challenge maybe in form of the antagonist, a situation, or other characters.

An event, revelation, or a new character that creates a problem the protagonist must overcome is called the: Conflict For example, in Harry potter stories, The main character need to overcome the threats that created by the most powerful wizard in the world before he finally achieve the life of peace that he always wanted.