Why do governments exist? One major reason is that they create rules. But what rules are necessary or desirable? That is open to question, and different types of governments have certainly created a wide variety of rules.
GOVERNMENTS almost certainly originated with the need to protect people from conflicts and to provide law and order. Why have conflicts among people happened throughout history? Many people, both famous and ordinary, have tried to answer that question. Perhaps human nature dictates selfishness, and people inevitably will come to blows over who gets what property or privilege. Or maybe, as KARL MARX explains, it is because the very idea of "PROPERTY" makes people selfish and greedy.
Whatever the reasons, governments first evolved as people discovered that protection was easier if they stayed together in groups and if they all agreed that one (or some) in the group should have more power than others. This recognition is the basis of SOVEREIGNTY, or the right of a group (later a country) to be free of outside interference.