Are there practical reasons for states--even the most powerful ones--to allow limits to their power?
While many argue that Thucydides was a political realist, emphasizing the importance of power and military forces, immediately following the Melian Dialogue, he begins the story of Athens' downfall. In the end, its absolute powers destroys it.
In the field of International Relations, the school of thought known as liberalism or idealism would argue that there are practical reasons for states to allow their powers to be limited. They would argue that, by doing so, states help to create an international order that makes peace more possible.
One of the basic tenets of idealism is that the international order does not have to be anarchic in the way the realists say it does. Idealists argue that states can and should willingly submit to rules imposed upon them by international agreements and by international bodies such as the United Nations. The theory holds that doing so will decrease the level of distrust in the world and make conflict less likely.
If this is the case, it is practical for states to submit to limits on their power. By doing so, they will actually be creating conditions that make war less likely. This will increase their security and likely prosperity.