The first point to note is that Russia does not have a territorial claim against Ukraine. It is true that Crimea was transferred from Russia to Ukraine in 1954, while both were part of the Soviet Union. However, when the Union dissolved in December 1991, Russia confirmed that it recognised Ukraine within the borders obtained at that point. It has restated this position in a whole series of binding treaties, including the 1994 Budapest Agreement which was meant to guarantee Ukraine’s integrity and security after it disowned nuclear weapons.

Even if there was a territorial claim, Russia would of course not be entitled to pursue it forcibly. The next question therefore is whether an unlawful use of force has occurred. Ukraine did consent in an agreement of 1997 to the presence of the Russian Black sea fleet in its Crimean harbours, including a large infrastructure of support facilities and bases. The agreement was originally supposed to run until 2017, but was extended by 25 years in 2010, in exchange for a settlement of Ukraine’s oil and gas bills owed to Russia.

Under the agreement, major movements of Russian forces require consultation with the Ukrainian authorities and the agreed force levels cannot be increased unilaterally. Contrary to these obligations, Russia has augmented its forces in Crimea without the consent of Ukraine. It has deployed them outside of the agreed bases, taking control over key installations, such as airports, and encircling Ukrainian units. Through these actions it has displaced the lawful public authorities of Ukraine and created space for the pro-Russian local authorities in Crimea to take full control. Legally, this clearly amounts to a significant act of armed intervention.

Presence = aggression?

Some may ask whether the mere presence of a foreign armed force operating without the consent of the local sovereign also amounts to a violation of the international prohibition of the use of force if no shot is fired. A UN definition of 1974 considers the use of foreign armed forces on the territory of a state in contravention of the agreement governing that presence as “aggression”. The concept of aggression is intended to guide the UN Security Council in its response to serious violations of the prohibition of the use of force under the UN Charter. Still, under present conditions an “armed attack”—the slightly different trigger-point in the UN Charter for the application of the right to self-defence—has probably not yet occurred. This may change, however, should the Kremlin annex the territory while continuing to forcibly exclude Ukraine from asserting its own sovereignty over it.

In fact, Russia may seek to tempt the Ukrainian authorities to move into Crimea. It would then assert the right to defend its troops and ethnic kin and conflict may spread into Eastern Ukraine. Of course, the author of an armed intervention cannot claim self-defence to maintain the unlawful status it has created. Nevertheless, the Ukrainian authorities are well advised to exercise extreme caution, as the fate of the Georgian provinces of South Ossetia and Abkhasia demonstrated in 2008. When Georgia attempted to restore its authority over them, Russia occupied the territories. Both declared nominal independence and have been virtually incorporated into Russia ever since.

Russia has oscillated somewhat in its legal arguments justifying its most recent action. On the one hand, it has denied that its forces have been involved in any unlawful activities in Crimea. On the other hand, it has formally invoked before the UN Security Council a letter from the displaced President of Ukraine, Viktor Yanukovich, requesting armed intervention. Moreover, Moscow claims that the existing interim government in Kiev is the illegitimate result of a Western-inspired coup.

Yanukovich agreement

The respective positions of the Ukrainian authorities, old and new, must be analysed in the context of the agreement reached between President Yanukovich and the leaders of the opposition on 21 February. That agreement was witnessed by the Foreign Ministers of Poland, Germany and France. Russia disowned it at the time, although it is now insisting on its implementation.

According to the agreement intended to end the civil revolt against Yanukovich, a new interim government would be formed. There would be an amnesty for the protesters and Parliament would replace the existing constitution with the version of 2004 within 48 hours. That version of the constitution provided for far more limited powers of the president. This would be followed by further constitutional revisions to be completed by September and fresh presidential elections before the end of the year.

Parliament assembled the following day, implementing the agreement, including the reversion to the 2004 constitution with a “constitutional majority”. In accordance with the agreement with the president, this was done in an accelerated procedure not foreseen in the constitution, to meet the agreed deadline of 48 hours. When it emerged that the president seemed to renounce the agreement he had signed the previous day and appeared to have disappeared from the country following the shootings of demonstrators and riots overnight, the Parliament decided unanimously to remove him from office.

Instead of the more time-consuming impeachment procedure, which would have also involved the Constitutional Court, Parliament applied Art 112 of the constitution. Admittedly, that provision covers death, incapacity or resignation of the president, rather than disappearance. As the president himself had agreed to the irregular restoration of the 2004 constitution, this technical defect seems less decisive in a situation of revolutionary change. Applying Art 112 in its version of 2004, the speaker of Parliament then took over as temporary president, with fresh elections foreseen for May.

Even if it is contested whether the president had been lawfully removed from office, it is clear that he certainly no longer had authority to represent Ukraine in relation to the use of force. He had lost effectiveness in relation to governance in Ukraine, and he had lost legitimacy to represent the state externally, having been unanimously disowned by the parliamentary representatives of the people of Ukraine, the true sovereign. In such a situation he could no longer exercise public authority to the extent of inviting intervention by the armed forces of the very state sheltering him abroad.

Russian arguments

President Putin also obtained authority from the upper house of the Duma to use force to protect ethnic Russians in the Crimea and the Russian forces stationed there. First, there is the argument of self-defence of Russian service-members in Crimea. The US invoked that argument to justify its intervention in Panama in 1989. As was the case then, this justification is not persuasive here. There were no armed attacks to which the Russian forces already stationed in Crimea could have responded.

The second argument would concern “rescue of nationals abroad”. Russia has in the past issued passports to ethnic Russians and even others in neighbouring territories. It later argued that it had a right to rescue them militarily, as happened in relation to the Georgian territories of Abkhasia and South Ossetia in 2008.

There is a long tradition of rescue operations of foreign nationals, mainly in situations of conflict and chaos in African states. However, in this instance, there was no evidence of such an emergency. Moreover, the EU Commission of Inquiry into the use of force against Georgia has denounced the practice of “passportization” of those to be rescued later as unlawful. Finally, rescue of nationals abroad justifies the extraction of nationals under threat. It does not justify the occupation of the territory they inhabit, or even its forcible incorporation.

The same applies to the final justification—protection of ethnic Russians or even of Russian speakers (in fact most Ukrainians speak Russian) in Crimea and possibly in other parts of Eastern Ukraine. The right of humanitarian intervention remains contested, at least in instances where the intervening state acts alone, in the absence of findings by objective international agencies confirming the existence of an overwhelming humanitarian emergency. In this instance, there was no such emergency.

Supporters of Moscow’s position have invoked the case of NATO’s intervention in Kosovo. However, in that instance, the UN Security Council had confirmed the overwhelming humanitarian emergency and a threat to international peace and security. NATO’s action was limited to achieving the humanitarian objectives expressed by the Security Council. It did not occupy the territory which was instead immediately transferred to neutral UN administration.

International law

Since the experience of Germany’s actions in the run-up to World War II, Europe has been very resistant to accept that a state can exercise special powers of protection for its ethnic kin in neighbouring territories. Hungary was severely criticised when it attempted to expand its legal protection to ethnic Hungarians living abroad. Instead, the emphasis has been on human rights and non-discrimination, and more recently on minority rights. Ukraine is a party to the European Framework Convention for the Protection of National Minorities and the European Charter on Regional and Minority Languages. The Council of Europe, the guardian of both treaties, has found Kiev to be in overall compliance with those standards. Indeed, it has complained that the heavy focus on the rights of Russian-language speakers in Ukraine has distracted from the entitlements of other groups.

Obviously, the international legal order is even more hesitant when it comes to the forcible incorporation of territory into neighbouring states on ethnic grounds. The Crimean Parliament has attempted to avoid this problem by first declaring independence, before holding its referendum on integration with Russia. This manoeuvre was also intended to remove Crimea from the restrictions of the Ukrainian constitution, which require a nation-wide referendum in relation to any proposed change of the territory of the state.

But moving the issue from the level of Ukrainian constitutional law to international law does not resolve the issue. International law recognises the right of self-determination and secession of colonial territories. The dissolutions of the USSR and the Former Yugoslavia have confirmed a right to constitutional self-determination where a federal state dissolves. Some argue that entities within states that have suffered prolonged and severe repression, or lack of representation in the state organs, might enjoy a right to remedial self-determination. But none of these categories apply to Crimea.

Crimea points to an Advisory Opinion given by the International Court of Justice at The Hague in response to Kosovo’s declaration of independence of 2008, suggesting that that international law does not preclude declarations of independence by secessionist units.

However, independence is the outcome of an extensive process, involving the exploration of alternatives to secession, such as enhanced autonomy, negotiating the question to be asked in a referendum, and discussing the terms of a possible divorce. In the case of Crimea, the declaration of independence has come suddenly, without any consultation and was obtained at gun-point.

Critics of the West argue that the US and others have committed similar offences, when intervening in Kosovo in 1999, when invading Iraq in 2003, or supposedly when exceeding a humanitarian mandate in Libya in 2012. Kosovo and Libya, at least, were different, as there were genuine humanitarian circumstances. Moreover, the failings of the one side do not excuse the offences of the other. And, crucially, Moscow’s actions, both in relation to Georgia and now in relation to the Ukraine, stand alone as the only instances where a state has forcibly changed European boundaries to its advantage.

Marc Weller is Professor of International Law in the University of Cambridge and Director of the Lauterpacht Centre for International Law. He is the editor of the forthcoming Handbook on the Use of Force in International Law (Oxford University Press). He practices at Doughty Street Chambers.