The Russian "invasion" of the Crimea offers an interesting precedent.

The Ukrainian president is removed from power by the Ukrainian people's elected representatives. Crimean citizens are Ukrainian, may speak Russian but are not Russian.

So, If Barack Obama is removed from power by the American people's elected representatives in Congress, then presumably Mexico may legitimately invade and occupy parts of the southern United States, on the grounds that there are, in Texas and California, large numbers of US citizens who speak Spanish but are NOT Mexican.

The consequences of this bit of Russian realpolitik could be far-reaching.

Trevor Rigg,

15 Greenbank Gardens,

Edinburgh.

The rapidity of events makes it difficult for the man in the street to follow events in the Ukraine.

Speaking in Paris, John Kerry, the US Secretary of State, outlined a lexicon of treaties he alleged had been breached by the Russians in Ukraine. There is one significant and relevant treaty that he omitted to mention. The Montreux convention Regarding the Regime of the Straits prohibits the passage of large naval vessels through the Bosporus. Non Black Sea states, in particular, are limited to displacement of not more than 15,000 tons. As the Obama Doctrine places the containment of China as the prime defence objective, the US would not wish to see their ironclads lost on the Black Sea floor.

I am unsure of the tactic of holding a plebiscite in the Crimea alone, excluding the rest of Ukraine east of the Dnieper. Russia may secure the Crimea and lose the rest of the country. With Nato bases across the border, the peninsula would be vulnerable, and the Black Sea fleet open to first strike attack.

I hope that Vladimir has studied the coordinates.

Jimmy Johnston,

38 Merryland Street,

Glasgow.