Empires may take decades to dismantle, as did Britain's through the 19th and 20th century. Or they may collapse almost overnight, as the Soviet empire did 17 years ago. But mentalities and memories are not erased so easily. Over-sensitivities have a tendency to linger, on both sides of the erstwhile imperial divide.
Consider the Russia-Ukraine gas dispute which – mercifully for the Balkan countries at the end of the pipeline – seems to be over for another year. This now annual quarrel, which escalates in proportion to the continent's winter freeze, has a colonial context. In Soviet times, Ukraine was a part of the empire, benefiting from cheap Russian energy in return for a proportion of its grain harvest, machine-building products and naval facilities. Oh yes, and a suitably respectful attitude towards the imperial power.
Three years ago, this imperial aspect was uppermost in much reporting. The dispute was seen as less about the price of gas than about Russia's desire to reassert control over a wayward colony trying to break free by way of the Orange Revolution. No mention of the then Russian President, Vladimir Putin, was complete without a reference to his – mistranslated – description of the Soviet collapse as "the greatest geopolitical catastrophe of the 20th century". The inference was that Russia should get over its imperial nostalgia.
This year's reporting was less partial, thanks perhaps to Russia's savvier PR and a generally harder-headed approach to commercial reality. Many noted not just Russia's abiding nostalgia for empire, but the way in which Ukraine "needled" its former suzerain, making demands that it knew perfectly well could not be met.
In fact, at official levels, these two neighbours have acquired an almost infinite capacity to irritate each other in a familiar big-brother, little-brother kind of way. Long years of dealing with an unequal reality have left their destructive mark – on both sides.
Russia and Ukraine, though, are hardly unique in their post-colonial ability to rub each other up the wrong way. We have a close equivalent of our own. For Russia, read the United Kingdom; for Ukraine, read the Republic of Ireland. Almost a century after Ireland became a separate state, we – that is we the British – are only now coming to terms with Ireland as a fully independent country.
If you don't believe me, ask why it is only this year, in the Borders, Citizenship and Immigration Bill introduced to Parliament last week, that there is provision for Irish citizens to be treated as foreign nationals. The Bill claimed most headlines for its proposed new requirements for British citizenship. But to my mind, this legislation contained something more interesting. It requires Irish citizens to show their passports to enter the UK, for the first time since the Irish Free State – now the Republic of Ireland – was founded in 1922.
Of course, it was always easy to regard ease of movement between the Irish Republic and the UK as evidence of a privileged, or special, relationship. And it was, without doubt, a convenience to regular travellers. The more you think about it, though, the more it also smacks of Britain's reluctance to recognise Ireland as a foreign country and the Irish as a separate nation.
The same applies to the right of Irish citizens, resident in the UK, to vote in British elections. Not just in local elections – which is permitted throughout the European Union – but in general elections. This is something else that speaks of Britain's refusal to let go.
There have been improvements over a generation, spurred by Ireland's economic success and the end of sectarian violence in the North. But Westminster still seems unable to cut the umbilical cord. The voting right is not affected by the new Bill; nor is the essentially open land border between the Republic and Northern Ireland. Is it not time that the UK brought itself to treat the Irish Republic as a separate and fully fledged country?
Perhaps the closer the imperial power is to a junior partner, geographically, linguistically and culturally, the more agonised the parting when it comes. With the dubious exception of Belarus, Ukraine was always the closest of the Soviet republics to Russia, and the one whose loss Moscow most resented. Inspiring affection and antipathy in equal measure, Algeria still occupies a special place in French hearts. It is all very well for us to tell Russia to get over its loss of empire. But if we are honest, we still haven't got over ours.