Russia's ruler Vladimir Putin has demanded that Ukraine adopt a federal constitution. The move is a gambit to gain Moscow more leverage in Ukraine.
Ukraine is diverse, but it is a distinct nation, with a right to independence from Russia; and, despite Russian claims, it does not divide neatly into two sectors.
The west is poorer, heavily dependent on remittances from Ukrainians working abroad, and mostly Ukrainian-speaking: it was not part of the USSR until 1939.
In the middle, Kiev, the capital, and centre of the movement which ousted the corrupt pro-Russian president Yanukovych in February, is mostly Russian-speaking. Rural areas are more often Ukrainian-speaking.
The eastern edge is the site of most of Ukraine's heavy industry and natural resources. It is more heavily Russian-speaking, and a significant minority are actually Russian. (Workers from elsewhere in the USSR moved to eastern Ukraine's factories and miners during Stalinist industrialisation).
Whether this diversity is managed by federal arrangements or not should be Ukraine's choice. Putin's government has no rights in the matter.
Since February Putin has militarily occupied and annexed Crimea and massed troops on Ukraine's eastern borders. As we go to press on 1 April, Russia is said to be reducing that military build-up.
Within Russia, itself theoretically a federal state, Putin has transferred the bulk of tax income to the centre, and abolished direct local elections for regional governors in favour of having them appointed from the centre.
On Saturday 29 March, representatives of Crimea's indigenous people - the Crimean Tatars, deported en masse by Stalin in 1944 and allowed to return to their homeland only in 1989 - met and voted to seek "territorial autonomy" within Crimea. Their experience under Stalin and Brezhnev has made the Tatars fearful of Russian rule, and most of them boycotted the rigged 16 March referendum to join Crimea to Russia.
New presidential elections in Ukraine are scheduled for 25 May. The front-runner is Petro Poroshenko, an oligarch of slight social democratic pretensions.
Russia: hands off Ukraine! Keep Russian troops out!
Western governments: cancel Ukraine's debts!
The labour movement should back Ukraine's left in its efforts to create "third pole" against both Russian imperialism and the Ukrainian oligarchs.