I spend much of my professional life reading the words of people who were passionate advocates of Union, and, indeed, who declared their willingness to die for it. Last night I gave a talk about my new biography of Abraham Lincoln, who was the most articulate advocate of Union of all. The audience, at the Ealing branch of the Historical Association, were very interesting in discussing the parallels between the crisis of the American Union in 1861 and the crisis of the Union of the United Kingdom today. Is there a sense in which history is repeating itself as farce? No slavery at stake — that’s pretty fundamental. But it could be said that many Yes voters in Scotland want to secede, like Southern secessionists in 1861, because they don’t like the result of an election: the General Election of 2010 delivering  a government with a power base in a region of the country with profoundly different values, just as the 1860 election put a Republican in the White House. A Union which had seemed to work well for all sides for many years has seen the splintering of the bonds of Union (shared public services and nationalised industries). In both cases practical experience of self-government is the lever for secession. And in both there is a gulf of understanding, fueled by consuming different media outlets, which led the pro-Union side to under-estimate the strength of disunionism.

I have learned two things, as a historian, from recent weeks and months of avidly consuming the news about Scottish secession. The first is the importance of emotion in shaping political choices. We all know this, of course — and there is a vast political science and social psychology literature on the topic. But in the debate over disunion we’ve seen it in sharp relief. The economic case for Scottish independence is dodgy to put it mildly, yet the well-reasoned warnings of the Better Together campaign have not resonated because they haven’t trumped the underlying power of identity. The fact that an independent SCotland sharing a currency Union with rUK would not really be independent at all, and would have, bizarrely, given up its representation in the government that was, among other things, still setting its interest rates, is beside the point if want you want to do is to express a rare sense of power by voting for a new polity. In a brilliant analysis of the referendum campaign Carol Craig fascinatingly explains how the SNP have used the psychology of optimism to drive their agenda, running roughshod over the material concerns that politicians usually focus on. Historians have long recognised the power of emotion in the crisis of disunion in the 1860s, but up until now I have not, as a writer and researcher, felt it myself, and understood it, as acutely as I now do. The language of family, divorce, separation — all highly emotional, but not cynically deployed (usually). People mean it. They feel it. (There are many examples of this, but I was especially struck by this brief piece by Jamie Reed, the Labour MP for Copeland.)

The second thing revealed by this whole extraordinary crisis of disunion is the importance of political judgment, and of, let’s face it, sheer luck. For generations to come, the judgement of all the leaders of the UK parties, but especially, since the buck stops with him, of Prime Minister David Cameron, will be picked over by historians. The precise question asked (had it been ‘Should Scotland remain in the United Kingdom?’ would that have made a difference?) the threshold for success (why not two thirds as in the devolution referenda?), the strategy of the campaign. On such matters the fate of countries can turn. Of course if you’re a Scottish nationalist you might say that independence is the natural and unstoppable will of the people — just as many in America in the 1860s saw the hand of Providence at work. But it’s amazing how Providence pivots on the decisions of fallible politicians.