Why does social inequality lead to social tension?

We all live in a social system in which people communicate with each other. The modern world presupposes the equality of all people in society. But it also happens that this equality is violated. For example, when one person gets more rights than another. Often this happens thanks to bandits who establish control over society in turbulent times, or when a dictator comes to power, a vivid example of this is Hitler and the society he built, which naturally does not suit society and puts it in a state of tension.