One of the greatest problems with foreign and defence policy is understanding the real motives for a state's action. No one knows Vladimir Putin's real intentions over Ukraine – perhaps not even the Russian leader himself. Any good liberal may hope that Putin is as respectful of international law as he claims, and that his interests extend merely to protecting the Russian-speaking minorities. However, the Geneva deal agreed between Russia and the west on Thursday is a thin reed that can mean too many things to too many people.
Start with the phrase: "All illegal armed groups must be disarmed." Who by? The west believes that the disciplined, well-armed and trained militants occupying government buildings in Donetsk, Kramatorsk, Mariupol and Slavyansk (where people were shot this weekend) are under Russian influence. The Kremlin denies it. The militants are not budging. One spokesman said they will only move when the Ukrainian government is replaced.
Take another piece of Geneva crack-covering: "The announced constitutional process will be inclusive, transparent and accountable." For Russia, that means a process of federalisation of Ukraine that – at the minimum – leaves it a neutral buffer state. For the Ukrainian government, it cannot rule out the prospect of EU membership.
In the long term, there may be a potential compromise for Ukraine in what is increasingly great power politics: devolved administrations for Russian-speaking regions, EU membership and neutrality outside Nato. Finland and Sweden are precedents for this model. Putin may note, though, that his handling of the Ukraine crisis has reopened the Finnish and Swedish debates on Nato membership.
What if Putin is more ambitious? His televised interview shortly before the Geneva deal was worrying. He hoped that it would not be necessary to use the powers he had been given by the federation council to invade Ukraine, but added: "These are all territories which in the [1920s] were handed over by the Soviet government. Only God knows why they did this." He also used the old phrase "New Russia" to refer to the arc of eastern and southern Ukrainian territory by the Black Sea.
Crimea was transferred to Ukraine in 1954, but "New Russia" has been part of Ukraine far longer. If any border adjustment as old as the 1920s is now to be up for grabs, Europe and the Middle East could become a tinderbox. Most of Europe's international borders date from 1919, when the Paris peace conference dismembered the German, Austro-Hungarian and Ottoman empires – dynastic states with scattered linguistic and ethnic groups.
Since then, European states have trod lightly around the possibility of redrawing boundaries, aware of the dangers and limitations of the principle then avowed by the US president, Woodrow Wilson, of "self-determination". Europe's patchwork of ethnic and linguistic minorities simply rules out clean-cut borders, which are a British (and insular) and American (and pan-continental) conceit.
There are German-speakers in eastern Belgium and the South Tirol area of Italy; Hungarian-speakers in Slovakia and Romania; Russian-speakers in all the Baltic states and Ukraine; Finnish speakers in Russia. One brave attempt to codify Europe's diversity found 87 "peoples of Europe" of whom just 33 were majorities in their own states. Some 105 million Europeans out of 770 million were "national minorities".
We mess with Europe's borders at our peril. There will never be a tidy or right answer. In common with many Ukrainians, Estonia's Social Democrat president, Toomas Hendrik Ilves, draws an explicit parallel with Hitler's wooing and then annexation of the Sudeten Germans in pre-war Czechoslovakia. The British and French agreed to the transfer in the 1938 Munich appeasement.
Ilves, whose country has a big Russian-speaking minority, warns that our whole thinking may have to change if we have been operating on the fundamental assumption that "you don't change borders through military intervention and you don't make this Sudetenland kind of appeal to co-ethnics".
Putin is no Hitler, but he is a former KGB officer with a strong sense of the Kremlin's prestige and power, and he is an authoritarian Russian nationalist. If his principles on Ukraine were universally applied across Europe, they would be a recipe for turmoil and bloodshed.
Putin's position contradicts Russia's own solemn 1994 commitment to Ukraine's borders (given in exchange for Ukraine's denuclearisation), and also his view of Chechnya, where he denies self-determination and asserts that Chechen territory is inalienably Russian.
Russian policy towards Chechnya has been appallingly ruthless and bloody. But the conservative Putin on Chechnya is a far safer neighbour than the radical Putin on Ukraine. Some sleeping dogs should be left to lie. Awake, European nationalism will not just bark, but bite.
Chris Huhne was formerly Liberal Democrat MP for Eastleigh and secretary of state for energy and climate change.