conflict
A serious disagreement or struggle between people or ideas.
Conflict is a serious disagreement or struggle between people, groups, or even within yourself. When two friends both want to be team captain and neither will back down, that's a conflict. When countries go to war, that's a much larger and more dangerous conflict.
Conflicts happen because people have different goals, beliefs, or needs that clash with each other. Your sister wants to watch one show while you want to watch another. Two nations both claim the same territory. A character in a story must choose between loyalty to a friend and telling an important truth. These are all conflicts.
As a noun, the word can describe external struggles, like an armed conflict between nations or a scheduling conflict when two important events happen at the same time. It can also describe internal struggles: you might feel conflicted about whether to join the soccer team or the drama club because you love both activities.
As a verb, conflict means to clash or not fit together. Your plans might conflict with your friend's plans.
Not all conflicts are bad. Stories need conflict to be interesting. Scientists often make breakthroughs by exploring conflicting evidence that doesn't match their theories. Learning to handle conflicts respectfully and finding compromises are important skills for school, friendships, and life.