The Budapest Memorandum on Security Assurances (1994) was signed by: the Russian Federation, the United Kingdom, and the United States, regarding the security of Belarus, Kazakhstan and Ukraine. Under the agreement, Belarus, Kazakhstan and Ukraine gave their nuclear weapons to Russia, in return for promises of sovereignty and security. It seems Russia has definitely violated points 1 and 2 of the agreement by invading Ukraine. From point 4, it seems that the US and UK are obligated to help, but unclear if they are obligated to defend Ukraine, if Russia uses nuclear weapons. Since Russia did not use nuclear weapons, point 4 may not apply. However, points 1 and 2 say that the sovereignty of Ukraine must be respected and force must not be used. But it does not say that the US and UK must defend the sovereignty of Ukraine.
1. Respect Belarusian, Kazakh and Ukrainian independence and sovereignty in the existing borders.
2. Refrain from the threat or the use of force against Belarus, Kazakhstan or Ukraine.
4. Seek immediate Security Council action to provide assistance to Belarus, Kazakhstan or Ukraine if they “should become a victim of an act of aggression or an object of a threat of aggression in which nuclear weapons are used”.
