Core Legal Answer & Context: State succession refers to the replacement of one state by another in the responsibility for the international relations of territory. This occurs when a state undergoes significant changes (e.g., merger, dissolution, secession, decolonization), raising questions about the fate of its treaties, debts, assets, and the nationality of its population.

Various Theories of State Succession:

1. Universal Succession (Old Theory): This theory, largely discredited in modern international law, posited that the successor state automatically inherits all rights and obligations of the predecessor state, including treaties, debts, and property. It treated the successor state as a continuation of the predecessor.
2. Partial/Clean Slate Theory (New States/Decolonization): This theory argues that a newly independent state (especially one emerging from decolonization) starts with a 'clean slate.' It is not automatically bound by the treaties or obligations of the predecessor state, unless it explicitly agrees to them. This allows new states to choose their own international commitments and avoid burdens imposed by colonial powers.
3. Continuity/Moving Treaty-Frontier Rule: For treaties, this rule suggests that when territory is transferred from one state to another, the treaties of the predecessor state cease to apply to that territory, and the treaties of the successor state begin to apply. This is common in cases of cession or annexation.
4. Uti Possidetis Juris: Primarily applied in decolonization, this principle states that newly independent states should retain the colonial administrative borders that existed at the time of independence. Its purpose is to prevent border disputes among new states.

Relevant Statutes and Sections:

1. Vienna Convention on Succession of States in Respect of Treaties (1978): Codifies rules for treaty succession, largely adopting the 'clean slate' for new states and the 'moving treaty-frontier' for territorial transfers.
2. Vienna Convention on Succession of States in Respect of State Property, Archives and Debts (1983): Deals with succession to property, archives, and debts, though it has not yet entered into force.

Important Landmark Cases:

1. Island of Palmas Case (Netherlands v. United States, 1928): While not directly on succession, it affirmed the principle of effective occupation and the continuity of sovereignty, which indirectly relates to how territorial rights are transferred or maintained.
2. The dissolution of the Soviet Union, Yugoslavia, and Czechoslovakia in the early 1990s provided practical examples of states applying these theories, often through specific agreements governing the succession of rights and obligations.

Clear Conclusion: Modern international law largely rejects universal succession. The 'clean slate' theory is favored for newly independent states, while the 'moving treaty-frontier' rule applies to territorial transfers. Succession to state property, archives, and debts is complex and often resolved through specific agreements, reflecting a pragmatic approach rather than a single overarching theory.