Among other things, Norman Davies’ Vanished Kingdoms is an investigation into the impermanence of power. He writes in his introduction:

The above observations may be worth considering further, if only because mainstream history-making persists in its addiction to great powers, to narratives about the roots of the present and to ultra-specialized topics. The resultant image of life in the past is necessarily deficient. In reality, life is far more complex; it consists of failures, near misses and brave tries as well as triumphs and successes. Mediocrity, ungrasped opportunities and false starts, though unsensational, are commonplace. The panorama of the past is indeed studded with greatness, but it is filled in the main with lesser powers, lesser people, lesser lives and lesser emotions. More importantly, students of history need to be constantly reminded of the transience of power, for transience is one of the fundamental characteristics both of the human condition and of the political order. Sooner or later, all things come to an end. Sooner or later, the center cannot hold. All states and nations, however great, bloom for a season and are replaced. (p.5)

He goes on to say that we all tend to deny that this impermanence applies to us:

Of course, human nature dictates that everyone is lulled into thinking that disasters only happen to others. Imperial nations, and ex-imperial nations, are particularly reluctant to recognize how quickly reality moves on. Having lived a charmed life in the mid-twentieth century, and having held out against the odds in our ‘Finest Hour’, the British risk falling into a state of self-delusion which tells them that their condition is still as fine, that their institutions are above compare, that their country is somehow eternal. The English in particular are blissfully unaware that the disintegration of the United Kingdom began in 1922, and will probably continue; they are less aware of complex identities than are the Welsh, the Scots or the Irish. Hence, if the end does come, it will come as a surprise. (p.6)

I suppose what makes it harder for imperial and ex-imperial nations to accept changing realities is that they suffer from the illusion that they have far more control over their fates than they actually do. They can remain attached to the illusion long after the control has slipped away, and indeed they hold onto the illusion because control has been slipping away. Especially when a nation defines itself in terms of its “mission” in the world or a cause to promote, it is in danger of losing itself when it no longer has the mission or cause to fall back to provide meaning.