Sovereignty is an important part of a nation state's government. Without it, the rights and liberties of its citizens are not fully protected by national or international standards. Also, the power and strength that the nation state holds is very important in the protection of the nation state.
1. Survival of the fittest
Sovereignty could provide public goods like standardization of weights and measures, standardization of coinage, tariff-free trade areas, binding regulation on trade, and an internal juridical hierarchy. A system of enforceable rules supported the development of a uniform and vigorous national policy on a wide range of issues including, crucially but not solely, the prosecution of wars.
2. Mutual empowerment
Identifiable sovereignty makes negotiations easier. One knows whom to talk to and what the decision is. The issue here is territorial juridiction as well as the ability to make credible commitments. Even when the Hanseatic League did develop common policies, it was unclear precisely to whom and where they applied. In the vital commerce with England, many cities cut independent deals at the expense of their fellow members. Hamburg, for example, acted like sovereign state when it applying special trade rules to its own ports. They behaved no differently in pursuit of these than sovereign states But the volatility of their internal politics made it difficult to for them to govern territory that was indispuitable theirs. When sovereign states recognized the city-states as members of the international system, it was almost always as weaker powers. The more consolidated their internal politics, they more they resembled miniature sovereign states.
REFERENCE
1. World Politics: Trends and Transformation 11th Edition , Charles W. Kegley,Jr.
2. John Locke, Standford Encyclopedia of Philosophy
3. Karl Marx,Political Science: A Primer, penulis Syed Serajul Islam and Abdul Rashid Moten