Richard English: If Brexit, rather than militant Irish republicanism, brings about end to partition, how will future view violence of the past?
The IRA's campaign kept the issue of the border on the political radar, but the Provisionals failed in their central goal: reunification
The border has famously re-entered politics, in Ireland and internationally. Northern nationalists, understandably angry at being removed from the EU mainly as a result of English votes and unionist preferences, have become markedly more anti-partitionist in their attitudes.
Indeed, it is one of the many ironies of Brexit that two expressly unionist parties - the Conservatives and the DUP - have done so much so quickly to erode the most important foundation that can exist for the Union of Great Britain and Northern Ireland: namely, nationalist acceptance of the partitioned northern state.
Will the United Kingdom survive? Scottish independence looks somewhat more likely now, post-Brexit, a potential development with its own profound effects on Northern Irish politics and tensions.
And the possibility of a border poll has substantially increased, as have the chances of unionists losing it in the foreseeable future.
All of this raises vital questions about the dynamics behind political change. If it is Brexit, rather than militant Irish republicanism, that turns out to stimulate the end of Irish partition, then how will the future view the violence of the past?
If there is, indeed, a border poll and the result favours a united Ireland, then would Ulster loyalists interpret the logic of Irish history as a justification for their own bloodstained resistance to this outcome?
Fifty years on from the eruption of the northern Troubles, we have perspective enough now to reflect systematically and calmly on such questions.
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Here are three points to consider as we do so. First, recent decades have shown strongly that political violence is not an essential element in major political change, such as that sought by nationalists who want to secede from the UK. Scotland, where there have been only tiny campaigns of nationalist terrorism, has come far closer in recent decades to leaving the UK than did a Northern Ireland state facing very sustained levels of Irish separatist violence. This has echoes elsewhere, too, with the Catalan-Basque comparison most obviously coming to mind.
Second, in Ireland itself, the record of political violence has to be considered in complex ways if we are to gain an accurate understanding of its effects and legacies. No simple "yes", or "no", can satisfy us when we ask the question "Does terrorism work?" in relation to Irish non-state violent campaigns. A better way to look at the issue is to think of the numerous different ways in which violence might potentially be considered to work: strategic victory, partial strategic victory, tactical successes, and the inherent rewards of violent campaigns.
Let's consider the case of the Provisional IRA - easily the most significant of the non-state actors in the Northern Ireland civil war of the past 50 years. The Provisionals ended their campaign in 2005 without securing their central, strategic goal of a united Ireland independent of British rule. Indeed, at the point of the armed struggle being brought to a close, public attitudes towards the post-1998 northern arrangements suggested that most nationalists, north and south, seemed comfortable with a reformed Northern Ireland as the basis for ongoing politics and society.
Moreover, the Provisionals' understandable strategic goal of defending northern Catholics also evaded them. Levels of violence against Catholics were actually much higher during the existence of the Provos' campaign, not least because of spirals of tit-for-tat violence, sometimes intensified by the IRA's own attacks.
So, strategic victory eluded the Provos during their 1969-2005 campaign. Some people have, therefore, suggested that the Provisionals simply lost the war and that their campaign achieved nothing of significance. But were there partial strategic successes secured by their violence? We cannot know with certainty whether UK governments and international partners would have prioritised reform in Northern Ireland to the extent that they did had there been no violence.
But we cannot simply dismiss the possibility that violence made radical change more pressing.
t certainly made the issue of Irish self-determination impossible to ignore.
It clearly made these issues more difficult to deal with, as well, of course, given the increased polarisation that terrorist and state violence always brings.
The relationships and trust required to achieve progress and compromise were made more elusive by violence on all sides, including that of the IRA.
But, in Ireland as elsewhere, partial strategic success for terrorist groups can involve them securing their secondary goals, whether the gaining of revenge or the sustaining of resistance, and here the Provisional IRA had significant returns.
In tactical terms, the IRA gained much publicity, undermined the UK and unionist states alike in crucial ways, and accrued organisational advantage for their movement. In terms of this last point, for example, when the peace process was under way, the Provos' capacity for violence gave Sinn Fein greater leverage with the UK Government than was possessed by the SDLP - something recently stressed again by former Deputy First Minister Seamus Mallon.
There are further complexities here, of course. Yes, the IRA gained publicity. But it was publicity secured by actions which people increasingly came to reject and abhor. As with so many other groups using terrorism throughout history, therefore, the most distinctive acts carried out - merciless violence - both gain fame and simultaneously diminish the widest range of support for the struggle.
There were huge costs paid by the IRA and their community in the Troubles. But there were also some sustaining rewards for volunteers: comradeship, purpose, excitement, a psychological shift from humiliating deference to proud defiance.
So, in assessing the violence of a major group like the IRA, we need a layered understanding. They failed to secure their central strategic goals, but they did attain other goods through violence. They made a problem more famously urgent of resolution, but also more lastingly difficult to resolve.
Behind this lies the third main issue for us to remember and it relates to morality and justification. Violence on all sides in the north - whether from the IRA, the UDA, the Parachute Regiment, or whoever - had behind it an explanatory context, which does not necessarily justify the appalling human consequences of that violence.
The long history of terrorism - in Ireland and elsewhere - repeatedly demands dispassionate analysis and calm explanation, set against the deep political problems from which such brutal actions emerge.
But, again and again, such violence turns out to have been far more certain to produce life-destroying awfulness than to bring about the benign, major political outcome that would be needed in order to justify it.
If there were to be a vote to end partition and establish a united Ireland, then this is arguably the most important point to be remembered on all sides from the polarising violence of the last 50 years in Ulster.
Richard English is Professor of Politics at Queen's University Belfast and author of Does Terrorism Work? A History (Oxford University Press)