Can Catalonia Achieve Independence Through a Unilateral Declaration of Independence Under International Law?



In the evening of October 10, 2017, Carles Puigdemont, the President of Catalonia gave a speech following the referendum on October 1, 2017 where the result showed that more than 90% of the voters chose to leave Spain. He said, “with the results of the referendum on October 1st, Catalonia has earned the right to be an independent state … the people have determined that Catalonia should become an independent state in the form of a republic.” According to Article 4(4) of Catalonia’s Law on the Self-determination Referendum, the affirmative outcome of the October 1 referendum gives the Catalan parliament the right to declare independence. However, instead of explicitly declaring independence, Puigdemont proposed that the Catalan parliament suspend the effects of the declaration of independence. This unclear statement has spurred reactions from the Spanish government demanding clarification and threatening to invoke Article 155 of the Constitution which gives the government broad powers to deal with a Self-governing Community upon approval of an overall majority of the Senate. While the tension between the region of Catalonia and Spain has increased tremendously, the situation also raises the question of whether secession through a unilateral declaration of independence is legitimate under international law.


Catalonia’s struggle for independence can be traced back to the early 15th Century when the region rebelled against the Kingdom of Aragon. The desire for independence continued after Catalonia became a part of Spain following the marriage between King Ferdinand of Aragon and Queen Isabella of Castile. In mid-17th Century, Catalonia unsuccessfully revolted against Spain, which resulted in abolishment of Catalan constitution and autonomy. In mid-19th Century, Catalan separatism movement reemerged again, and efforts were made to revive the Catalan language to strengthen their distinct cultural identity. The Catalan nationalist movement continued to grow into the 20th Century. Finally, in September 1932, Catalonia’s autonomy within Spain was legally established, and in 1979 Catalonia gained full autonomy. However, in the 2010 opinion, the Constitutional Court of Spain modified the Statute of Autonomy of Catalonia which grants a “nation” status to Catalonia, ruling that Catalonia was not a nation even though Catalans could constitute a nationality. Today, Catalonia is one of the most developed regions in Spain. Dissatisfaction towards Spain’s financial policy pushed the independence movement even further—an unofficial referendum was held in 2014 and an official one was held October 1, 2017.

Some commentators argue that there has been a wave of independent movements in recent years. For example, the Kurdish independence movement against Iraq is going on simultaneously with Catalan independence movement, and a Scottish independence referendum was held in 2014. Whether a unilateral declaration of independence is legitimate is a question of both domestic constitutional law and international law. Under domestic law, unlike the Scottish referendum which was recognized by the British government, the Constitutional Court of Spain decided that the referendum was illegal. Under international law, the answer to whether secession through a unilateral declaration of independence is legitimate is more complex than it seems on the surface.

To simplify the analysis, the answer lies in the tension between the right of self-determination and the right to territorial integrity, both of which are stated separately in Article 1 and 2 of Chapter I of the Charter of the United Nations. The International Court of Justice’s (ICJ) 2010 advisory opinion on Kosovo’s unilateral declaration of independence demonstrates the difficulty in deciding the legality of such declaration of independence. Instead of directly answering the question whether Kosovo has the right to independence through a unilateral declaration of independence, the ICJ framed the question to be whether international law prohibits such declaration of independence.

In paragraph 79 of its opinion, the ICJ recognizes the right of self-determination for “the peoples of non-self-governing territories and peoples subject to alien subjugation, domination and exploitation.” The ICJ also pointed out that such rights are commonly understood in the context of colonialism and the independence of former colonial territories. For a declaration of independence outside of this context, the ICJ, in paragraph 84, ruled that general international law does not prohibit such declaration. The ICJ reasoned that even though the United Nations Security Council issued resolutions condemning situations which involve unilateral declarations of independence, the resolutions condemned only the aspects of unlawful use of force or other violations of international law rather than the aspect of unilateral declaration. Therefore, Kosovo’s unilateral declaration of independence did not violate general international law.

Responding to the argument that the principle of territorial integrity implies a prohibition of unilateral declarations of independence, the ICJ, in paragraph 80, stated that the principle only imposes an obligation on states not to interfere with other states’ territorial integrity and political independence. However, the ICJ did not end its analysis there and saw the necessity of analyzing the issue under both Security Council Resolution 1244 (1999) and the United Nations Interim Administration Mission in Kosovo (UNMIK), which provides the constitutional framework in the Kosovo situation.

The ICJ found that neither documents prohibited Kosovo’s unilateral declaration of independence and eventually declared that Kosovo’s unilateral declaration of independence does not violate international law. The ICJ’s analysis shows that the legality of unilateral declarations of independence outside the context of colonialism is not a well-established principle in international law. If the legality of unilateral declarations of independence was well established in international law, the ICJ would not have needed to devote a substantial part of its opinion arguing that Kosovo’s declaration does not violate either the Resolution 1244 and the UNMIK.

Another important case that is helpful to answer the question of whether Catalonia’s unilateral secession is legal is Reference re Secession of Quebec. The Canadian court found that the right to self-determination is only applicable in the context of colonialism; outside of such context, self-determination can only be achieved within the framework of existing states. The court ruled that “A state whose government represents the whole of the people or peoples resident within its territory, on a basis of equality and without discrimination, and respects the principles of self‑determination in its internal arrangements, is entitled to maintain its territorial integrity under international law and to have that territorial integrity recognized by other states.” Applying this rule, the court decided that Quebec could not secede from Canada by a unilateral declaration of independence because Quebecers were not oppressed, colonized, or “denied meaningful access to government to pursue their political, economic, cultural and social development.” Unlike the ICJ, the Canadian court took the approach that the principle of territorial integrity prohibits unilateral declaration of independence unless the situation satisfies requirements that could invoke the right of self-determination. This view is supported by commentators who argue that unless authorized by the state’s constitution, unilateral declarations of independence are illegal.

Applying these rules to the situation in Catalonia, Catalonia cannot legally secede from Spain through a unilateral declaration of independence alone even though the declaration does not violate international law. Despite its long history of fighting for independence, Catalonia was not colonized or oppressed, and was granted a high degree of autonomy by the Spanish government. Its status does not rise to the threshold that the right of self-determination could be invoked. According to Reference re Secession of Quebec, the only way for Catalonia to become an independent state would be through Spain’s authorization and recognition. This option is unrealistic because the Constitutional Court of Spain has already decided that Catalonia has no right to declare independence. Moreover, under ICJ’s 2010 advisory opinion, Catalonia’s argument would be weak because unlike the Kosovo situation where the UNMIK (setting the constitutional framework for Kosovo) did not prohibit the declaration of independence, the October 1 referendum, which legitimatizes a declaration of independence, is deemed unconstitutional under the Spanish Constitution. Therefore, even if Catalonia eventually makes an explicit unilateral declaration of independence, it cannot achieve independence simply through such declaration.


Xi (Brooke) Zheng is a second-year J.D. student at Columbia Law School. She holds a Master of Arts in International Studies from University of Denver and a Master of Law in Human Rights from The University of Hong Kong.