1. Core Legal Answer & Context: The general rule in the law of treaties regarding third states is encapsulated in the Latin maxim pacta tertiis nec nocent nec prosunt, meaning "treaties neither harm nor benefit third parties." This fundamental principle, enshrined in Article 34 of the Vienna Convention on the Law of Treaties (VCLT), asserts that a treaty creates rights and obligations only for the states that are parties to it. A third state, which is not a party to the treaty, cannot be bound by its provisions, nor can it claim rights under it, without its consent. However, international law recognizes specific exceptions and mechanisms through which treaties can, under certain conditions, affect third states.

Imposition of Obligations on Third States (Limits): Article 35 of the VCLT states that an obligation arises for a third state from a provision of a treaty only if the parties to the treaty intend the provision to be the means of establishing the obligation and the third state expressly accepts that obligation in writing. This requirement for express written consent is a strict limit, reflecting the sovereign equality of states and the consensual nature of international law. Without such explicit acceptance, a treaty cannot unilaterally impose burdens on a non-party.

Conferral of Rights on Third States (Extent): Article 36 of the VCLT provides a more flexible approach for the conferral of rights. A right arises for a third state from a provision of a treaty if the parties to the treaty intend the provision to accord that right either to the third state, or to a group of states to which it belongs, or to all states, and the third state assents thereto. Assent is presumed so long as the contrary is not indicated, unless the treaty otherwise provides. However, a state exercising such a right must comply with the conditions for its exercise provided for in the treaty or established in conformity with the treaty (Article 36(2)). This means that while consent for rights is presumed, it is not entirely unconditional.

Exceptions and Other Considerations:

• Customary International Law (Article 38 VCLT): A treaty provision can become binding on third states if it reflects or generates a rule of customary international law. In such cases, the obligation or right for the third state arises not from the treaty itself, but from the customary rule, which is binding on all states (except persistent objectors). Treaties can play a significant role in the formation of custom by codifying existing custom or by providing the basis for new customary rules through widespread and consistent state practice accompanied by opinio juris.
• Objective Regimes: Some scholars argue for the existence of "objective regimes" or "territorial regimes" created by treaties (e.g., treaties establishing international waterways, demilitarized zones, or territorial settlements) that are binding on all states, regardless of their participation. However, this concept is debated, and its application is generally limited to specific contexts where the treaty creates a status or regime that is inherently universal in its effect.
• UN Security Council Resolutions: Treaties adopted under the authority of the UN Security Council (acting under Chapter VII of the UN Charter) can create obligations for all UN member states, including non-parties to the specific treaty, if the UNSC resolution makes the treaty's provisions binding. This is an indirect way for a treaty to affect non-parties, through the binding force of the UNSC resolution.

2. Relevant Statutes and Sections:

• Vienna Convention on the Law of Treaties (VCLT) 1969:
  • Article 34: General rule regarding third States (pacta tertiis nec nocent nec prosunt).
  • Article 35: Treaties providing for obligations for third States (requires express written consent).
  • Article 36: Treaties providing for rights for third States (assent presumed unless indicated otherwise).
  • Article 37: Revocation or modification of obligations or rights of third States.
  • Article 38: Rules in a treaty becoming binding on third States through international custom.

3. 1-2 Important Landmark Cases:

• Free Zones of Upper Savoy and the District of Gex Case (France v. Switzerland) (PCIJ, 1932): This case affirmed that a treaty could create rights in favor of a third state if that was the clear intention of the contracting parties, and the third state assented to it. The Permanent Court of International Justice stated that "it cannot be lightly presumed that stipulations favourable to a third State have been adopted without any intention of creating a legal right in its favour."
• North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands) (ICJ, 1969): While primarily concerning maritime delimitation, this case extensively discussed the conditions under which a treaty provision could become a rule of customary international law, thereby binding non-parties to the treaty. The ICJ clarified that for a treaty rule to become custom, it must be of a fundamentally norm-creating character, accompanied by widespread and virtually uniform state practice, and opinio juris (a sense of legal obligation).

4. Clear Conclusion: The extent to which a treaty can confer rights and impose obligations on a third state is strictly limited by the principle of pacta tertiis nec nocent nec prosunt. While obligations require the express written consent of the third state, rights can be conferred with presumed assent, provided the intention of the treaty parties is clear. The most significant way a treaty can affect non-parties is when its provisions evolve into rules of customary international law, binding all states irrespective of their treaty adherence. These mechanisms reflect a careful balance between the consensual nature of treaty law and the broader development of international legal norms.