THE Westminster terrorist attack and the death of Martin McGuinness last week have between them raised vital questions about terrorism and the pursuit of political change. The brutal incidents in London loudly proclaimed that jihadist violence remains an issue of potential lethality in Britain. And the passing of one of the Provisional IRA’s former leaders also challenged us all to reflect on what terrorism means for society and politics in these islands.

McGuinness would have condemned Wednesday’s London assault. This may seem ironic, given he had been for many years a leading figure in the IRA. The Provisionals killed many hundreds in pursuit of an independent and united Ireland, and they themselves repeatedly attacked establishment targets in England.

In his later years, however, Martin McGuinness became a major player in the peace process which has transformed and largely ended the violent Northern Irish conflict.

That latter phase of his career saw him clearly denounce ongoing violence. So when dissident Irish Republicans killed two soldiers and a Northern Irish police officer in March 2009, McGuinness declared these republican killers to be “traitors to the island of Ireland” – a brave statement for an ex-IRA man to make about Irish republicans who had killed members of the British security forces.

And one of the ironies of the world which McGuinness has left behind him is this: the part of the UK that is most likely to leave the United Kingdom is not the part in which he and his IRA comrades killed hundreds in order to secure withdrawal. It’s Scotland, where nationalists have a very realistic prospect of seceding from the UK after a campaign in which no blood has been spilled.

And this echoes other settings. The part of Spain

most likely to leave that state is not the Basque Country, where ETA separatists killed many people in pursuit of independence. It’s Catalonia, where peaceful mobilisation has been the foundation for separatist momentum. Does all this have lessons for how we think about the pursuit of political change in the 21st century? I think it does.

First, there is a wider pattern evident in the history of terrorism which suggests that, in the vast majority of cases, terrorist groups fail to achieve their central, primary goals. There are exceptions. So Zionist terrorists of the 1930s and 1940s could claim that their violence accelerated the establishment of the state of Israel. And the FLN (National Liberation Front) in Algeria could also make a claim that their terrorism had substantial success in relation to their strategic goals against the French during the 1950s and 1960s. But these examples represent the minority of cases. And in the wake of Wednesday’s atrocity in London, it is important to remember how rare it is for terrorists to achieve their central goals. Overwhelmingly – from the PLO (Palestine Liberation Organisation) to al-Qaeda, from the FARC (Revolutionary Armed Forces of Colombia) to the far-left Baader-Meinhof Group in Germany – a more common reality has been that terrorist groups do not secure their central, primary goals through violence.

Much of this has to do with the ambiguous effects of publicity, something evident again last week in London. There’s no doubt that terrorist violence seizes attention and grabs the headlines. But, as the IRA and ETA both found out, this publicity can backfire on you politically, since it tends to generate much revulsion against the cause and against the perpetrators of merciless violence.

In fact, what terrorist groups tend more often to achieve is at a lower level of success. There can be partial strategic success. Martin McGuinness himself used to claim that, although a united Ireland had not been achieved, the advances that the Irish nationalist community in the North of Ireland enjoyed were partly built on the struggle that the IRA had carried out.

This is a debatable claim, given that so many Northern Irish nationalists believed that progress could be made without bloodshed. But terrorist groups do often achieve partial progress, and they can also succeed in achieving their second-level goals. So, Hamas are very unlikely to destroy the state of Israel and produce an Islamic Palestinian state in its place. But they have succeeded in the secondary goal of inflicting revenge upon Israelis, and they have also ensured the secondary aim of sustaining Palestinian resistance into the future. Without justifying violence, such successes do partly explain that group’s continued vibrancy.

Wednesday’s attacker in London will not greatly alter UK foreign policy; but he did inflict vengeful violence on what he clearly thought to be a deserving enemy, and securing that second-level aspiration of revenge echoes much terrorism throughout history.

At a lower level still, terrorists can often achieve what might be termed tactical successes. The 9/11 atrocity was a strategic failure, in that it did not bring about al-Qaeda’s central goals of expelling the United States from influence in the Muslim world, or replacing Muslim regimes with political authorities that were more to Osama bin Laden’s taste. But there is no doubt about the tactical-operational success of those brutal 2001 attacks.

Similarly, much of the appeal of terrorism as a method lies in its capacity to generate huge publicity – another tactical-level success – and to undermine terrorists’ opponents. If Hamas can prompt Israel into what many people see as heavy-handed repression, then this can undermine Israel in the eyes of the international community. Sharper-eyed terrorists throughout history have recognised this pattern: that you can provoke a state into undermining itself in response to terrorist violence.

Nor should it be ignored that there exist what might be called the inherent rewards of terrorist activity. These can involve prestige, fame, the psychological rewards of righteous struggle, the financial rewards that some people gain through their violence, and also a sense of comradeship and adventure. Martin McGuinness himself referred to his youthful IRA days with the words: “When you’re young, at that age, it’s quite exciting. There was a really exciting aspect to being on the run, living from house to house and travelling about.”

So terrorist groups have historically been more likely to achieve tactical successes, to bring about fulfilment of their secondary goals, and to derive inherent rewards, than they have been to secure their central, primary objectives. And this brings us to our second point: the reason for people like Martin McGuinness changing political direction owes far more to questions of effectiveness than it does to questions of morality or a change of heart.

McGuinness had once believed that IRA violence would force British withdrawal from Northern Ireland. In 1984 he had claimed that it was the IRA’s “war against British forces that will eventually bring Britain to withdraw. If Sinn Fein were to win every election it contested, it would still not get an agreement on British withdrawal”. Instead, McGuinness argued that “only disciplined revolutionary armed struggle by the IRA will end British rule”.

By the early 1990s he had come to recognise that this was not in fact the case. There seemed no prospect of the London Government giving the IRA what it most wanted, namely British withdrawal and a united Ireland. Nor was there any sign that Northern Ireland’s unionist majority was losing any of its commitment to remain in the UK. I’ve never met a more pragmatic group of people than the IRA members whom I’ve interviewed over the years. When people like Martin McGuinness recognised that violent Plan A was not working, they pragmatically began to look for an alternative mode of struggle. And it was this development that generated the Northern Ireland peace process.

This also has profound implications for other conflicts around the world, including jihadist campaigns against the West. It implies that even longstanding conflicts can come to some kind of end. It suggests that when the leadership of terrorist organisations recognises that terrorism is not producing victory, then alternative processes and political methods can sometimes be adopted. And, as in Northern Ireland, it suggests that compromises sometimes can be reached which give nobody full victory, but which give enough to most people for them to approve of a dignified ending to the violence.

Not all conflicts can be negotiated to a conclusion. But the failure of terrorist violence to achieve victory can over time diminish its popularity with adherents to the cause. There’s also a third aspect to all this, and this one has a strong Scottish dimension to it. Settings of endemic violence – Northern Ireland, Israel/Palestine, the Basque Country, Colombia, Iraq, Afghanistan, Syria – illustrate very painfully just how polarising terrorist violence tends to prove. Even the comparatively successful Northern Ireland peace process still has to contend with violently drawn division between mutually hostile communities. The experience of loss by so many people makes this entirely understandable. Terrorism tends not to achieve its central strategic goals; it does tend to divide communities against themselves and to make trust and compromise more difficult.

This is why the non-violent nationalism of contemporary Scotland is something to be respected for its peacefulness, whether or not one sympathises with its goals. What we can observe is that, whatever the eventual outcome of political divisions, the capacity to build constructively and to unite people is far more difficult if the violent path has been chosen.

And even where terrorist organisations seem to have secured strategic victory, the costs of their method of struggle can be painfully obvious, as the post-independence histories of Israel and Algeria make bloodily clear.

There’s nothing inevitable about the choices that political movements and political individuals make. While the IRA were engaged in a very sustained campaign of violence in Ireland, the non-violent Irish nationalists of the Social Democratic and Labour Party (SDLP) argued instead that “the Provisional IRA can achieve nothing by carrying on their campaign of violence but they can achieve almost anything they desire by knocking it off”.

The irony here is that what so many people have been celebrating about Martin McGuinness the peacemaker was his adoption of this SDLP-style approach. In other words, the genius of his latter-day contribution rested on his implicit recognition that his non-violent rivals within Irish nationalism had been right all along.

What does this mean for Scotland, and for wider questions of the pursuit of important political change in a world that is anxious about terrorism? It suggests that we should recognise the preciousness of political divisions which have not become violent. And that we should do all we can to engage respectfully with opponents in settings of political disagreement. Put another way, let’s not take for granted what a valuable thing it is to have peacefully expressed disagreement about an issue such as Scottish independence, and let’s ensure that debates, arguments and divergent opinions do not stray into aggressive or abusive territory. Whichever way the Scottish independence argument goes in coming years, we can see from neighbours in Northern Ireland and from attacks such as the one that occurred in London last week, what a heavy cost there is to aggressive pasts.

And above all let’s be prepared to recognise the limits of violence as a means of achieving change. This applies to states as well as non-state groups, I think. One of the ironies of the post-9/11 US-led War on Terror was that both sides – al-Qaeda, and their state opponents – found that their violence tended to undermine their public popularity. One of the key reasons for al-Qaeda not gaining as much Muslim support as they had hoped for was that so many of the world’s Muslims were repulsed by al-Qaeda violence, especially against civilians. It’s interesting to note how much sympathy there has been for Britain and for the British authorities in the wake of Wednesday’s London attack. But it’s also true that the USA lost much international credibility by an initial over-reliance of military methods in responding to the jihadist threat. The danger of such methods prompting anger and hostility can be seen in current US and allied violence in Syria against Isis, when civilian casualties are generated.

Martin McGuinness’s capacity to help shift the Irish republican movement from war to peace deserves huge respect, and the benefits of ending that violence are underlined when we witness the terrible suffering of the London victims of terrorism this week. McGuinness showed courage and resolute commitment to the eventual peace process in Northern Ireland, and that was a major contribution. But his career also demonstrates the invaluable benefits of avoiding blood-stained violence in nationalist and other conflicts. His political party, Sinn Fein, has become far more popular and effective since it turned away from supporting violence. And that is a vital lesson for future politics, whether in Scotland, Ireland or further afield in a century still marred by terrorism.