Tell me where international law permits annexation. I'd love to see it. As far as I was taught in law school, the Declaration on Friendly Relations and Co-operation among States, interpreting the UN Charter, states: "The territory of a State shall not be the object of acquisition by another State resulting from the threat or use of force. No territorial acquisition resulting from the threat or use of force shall be recognized as legal." Now, you might have an argument for why it's not territorial acquisition in this case (part of British mandate etc.), but annexation of territory won in war is generally illegal under int'l law.
U.S. sanctions Russia's state-owned arms exporter Rosoboronexport (Reuters)