Plato promoted a government based on virtue and justice, one that should lead to the common good of everyone in the polis (city-state), including the noble, rich and poor. This ideal is most identifiable as a philosophic meritocratic aristocracy or monarchy.
In the Republic and Laws, Plato lays out ideal states, not necessarily ones that can be implemented in reality, but ones that could be used as guiding forms. Plato's dialogues describe different types of governing that might lead to peace based on its value, not on its factional benefits. Plato believed that conflicting interests could be harmonized in an ideal society, without the expense of one or another faction. Each social class has different values, concerns and claims to rule, but Plato had observed, in his own time, the damage that unchecked governments of any type could cause their own citizens and others.