What is the position of the United Nations on state mergers?

Question

In general, the trend in recent years has been toward countries splitting into smaller independent entities. However, the opposite is also possible. For instance, suppose that tomorrow the European Union decided to become the United States of Europe, or continental North America united as Mexuscan. Does international law have a clear position on this?

In particular, has the United Nations taken an official position, through General Assembly resolutions or otherwise, on voluntary mergers of two or more member states?

Answer 1

North and South Yemen (YAR and PDRY) merged in the same year as Germany (1990).

And they both had UN seats until then (PDRY since 1967; YAR [as a Kingdom initially] since 1947--I'm not 100% when/if the Kingdom's seat was transferred to YAR's government, but I presume it was at some point.)

And at least this (1990 Yemeni) unification was explicitly welcomed by the UNGA in resolution 45/193, adopted on Dec 21, 1990.

The main purpose of the resolution (in the remainder) was to solicit economic aid for the unified Yemen.

So yes, there are even examples of the UNGA explicitly welcoming mergers of two states.

(The US had the PDRY on its list of terrorist states until the end, so that made it more difficult for the West to send aid there, I guess. Which might in part explain the resolution.)

Note that unlike in the case of Germany, the two Yemens had fought two border wars, although the unification was peaceful. There's a good backgrounder here by a IR prof which additional says that "unlike Germany, Yemen was a true union of equals [...] When the union occurred, they [both YAR and PDRY] both formally ceased to exist [and] an entirely new state came into being". Unlike Germany, the new/unified Yemeni state adopted a new constitution (drafted in late 1989). Despite the "new state" status (they themselves perceived), the new Republic of Yemen was not required to reapply to the UN for membership. The date of UN admission of the RoY was put back to 1947 (that of the YAR/Kingdom), but the their UN rep kept was that of PDRY (whereas the US ambassador kept was that of the YAR).

Answer 2

Does international law have a clear position on this?

Yes. Sovereign states are traditionally free to do just about anything, including merge. The UN charter does not change this. It says "The Organization is based on the principle of the sovereign equality of all its Members" (Article 2(1)).

The UN was born out of a desire to reduce the tendency for sovereign states to resort to war to settle their disputes. The charter's first two articles are full of statements to that effect:

Article 1

The Purposes of the United Nations are:

1. To maintain international peace and security, and to that end: to take effective collective measures for the prevention and removal of threats to the peace, and for the suppression of acts of aggression or other breaches of the peace, and to bring about by peaceful means, and in conformity with the principles of justice and international law, adjustment or settlement of international disputes or situations which might lead to a breach of the peace;
2. To develop friendly relations among nations based on respect for the principle of equal rights and self-determination of peoples, and to take other appropriate measures to strengthen universal peace;
3. To achieve international cooperation in solving international problems of an economic, social, cultural, or humanitarian character, and in promoting and encouraging respect for human rights and for fundamental freedoms for all without distinction as to race, sex, language, or religion; and
4. To be a center for harmonizing the actions of nations in the attainment of these common ends.

Article 2

The Organization and its Members, in pursuit of the Purposes stated in Article 1, shall act in accordance with the following Principles.

1. The Organization is based on the principle of the sovereign equality of all its Members.
2. All Members, in order to ensure to all of them the rights and benefits resulting from membership, shall fulfil in good faith the obligations assumed by them in accordance with the present Charter.
3. All Members shall settle their international disputes by peaceful means in such a manner that international peace and security, and justice, are not endangered.
4. All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.
5. All Members shall give the United Nations every assistance in any action it takes in accordance with the present Charter, and shall refrain from giving assistance to any state against which the United Nations is taking preventive or enforcement action.
6. The Organization shall ensure that states which are not Members of the United Nations act in accordance with these Principles so far as may be necessary for the maintenance of international peace and security.
7. Nothing contained in the present Charter shall authorize the United Nations to intervene in matters which are essentially within the domestic jurisdiction of any state or shall require the Members to submit such matters to settlement under the present Charter; but this principle shall not prejudice the application of enforcement measures under Chapter VII.

None of this precludes a peaceful merger of two members. The only question would be whether the resulting state required admission through the mechanism specified in Article 4. In 1990, the German Democratic Republic ceased to exist and the Federal Republic of Germany absorbed its territory, retaining its membership in the United Nations.