In the introduction to the book Nations and Nationalism, the historian Eric Hobsbawn imagines just how confusing the history of planet Earth would appear to an intergalactic historian landed on Earth in the aftermath of a nuclear Armageddon.

He describes how without understanding the concept of the nationstate or of nationalism the unfortunate alien could have no real understanding of the planet this last few centuries. He would find this little island an especially bleak and confusing place, bearing in mind the profound changes which nationalism has brought to this island and its people in this time.

Prof Fred Halliday, in his Turkel Opsahl Memorial lecture in 1997, gave a wonderful outline of the two conflicting nationalisms on this island - Catholic Irish nationalism and Protestant unionism. Opsahl was a Norwegian professor who headed a commission in Northern Ireland in 1992 on public opinion on "the way forward".

However, to return to Prof Halliday and how he outlined how Protestant unionism, despite the fact that it terms itself British and does not call for independence, remains essentially a form of nationalism.

He describes how unionist discourse talks of a Protestant nation and how the Britishness proclaimed by unionists concerns an identity, and a community as opposed to a shared population with the rest of the UK. It is a nationalism which has exercised its right to self-determination by adhering to the UK, just as Catholic Irish nationalism exercised its self-determination in opting for political independence.

In an important book on the understanding of the negotiations leading to the Good Friday agreement, The Far Side of Revenge by Deaglan de Breadun, Foreign Affairs Correspondent of this newspaper, he states:

"Reynolds was the catalyst for the first significant public development in the peace process, the Downing Street Declaration signed by himself and Major on December 15th, 1993.

In this document Britain reaffirmed its longstanding pledge to place the constitutional future of Northern Ireland in the hands of the people of the region, who could decide by a majority vote to enter a united Ireland if they so wished . . ."

On our little island, as we have seen again this week, the power of these nationalisms has moved people to kill, maim and riot. This week, once again, we have seen the parties in the North of this island march to the brink and beyond. It has seemed at times this past while that we are slipping back to the blind nationalism of the past. Regressive actions such as Sinn Fein's failure to push the agenda of decommissioning and Jeffrey Donaldson et al's intransigence could very well lead to an about-turn into the desolation of the Troubles.

The two traditions, the two nationalisms on this island, have so much in common. Our history is intertwined.

It is interesting to note for example, that Edward Carson, the father of Ulster unionism, had a Dublin accent and that his cousin, Mary Butler, gave the name Sinn Fein to Arthur Griffith's tiny band of dual monarchists.

When Carson formed the UVF, Patrick Pearse was delighted that he had done so. "I am glad that the Orangemen have armed, for it is a good thing to see arms in Irish hands." The Irish Volunteers mimicked Carson's Ulster Volunteers. Both Pearse and Carson were moved by that same militarism which had swept all Europe, which would bring blood sacrifice to the GPO and to the Somme alike in 1916. Such symmetry runs through the last century.

Just as Catholic Irish nationalism denied the validity of the Ulster unionist decision to remain within the UK, unionists denied the aspiration of 3 million Irish nationalists for Home Rule. We have shadow-boxed each other for a century at least.

Since then there has been a century of effort to find some kind of accommodation with one another; Craig-Collins, O'Neill-Lemass, Sunningdale, the Anglo-Irish Agreement and finally, at last, the Good Friday agreement.

Through the agreement we have accepted the validity of each other's ambitions. To borrow a phrase from the Progressive Unionist Party leader, Mr David Irvine, we are moving away from "cul-de-sac politics".

It has been a painful process. The loss of Articles 2 and 3, for example, was not easy for many of us. When I entered the Dail in 1965, I would have been strung up for such a notion, regardless of the quid pro quos from the other side. In the "wrap the green flag around me" atmosphere of the 1966 commemoration of the Easter Rising the Good Friday agreement would have been unthinkable.

The same is true north of the Border where, for example, William Lowry, a Stormont Minister for Home Affairs, when questioned by Orangemen about allowing an Orange hall to be used by the US army for a Catholic religious service, replied that it could always be "fumigated". Thankfully, we have all advanced with time towards the only rational, acceptable compromise, the Good Friday agreement. Because it is an equitable and fair compromise and there is simply no other deal in town.

Bigots on both sides who refuse to respect that equilibrium have to be resisted. I sat across from David Trimble and other Unionist leaders during the Good Friday agreement negotiations. We fought like cats and dogs, we disagreed, we bargained. But at the end of the day we found that middle ground where peace can survive. They left those negotiations with their unionism intact, with their right to remain within the UK, with the central tenets of their Protestant unionism intact, just as we left with our Irish nationalism intact.

But for the first time we found a way for the two nationalisms to coexist, we found a way to respect the legitimacy of the two nationalisms. It would be unacceptable now to back away from that respect, to return to the past, which is unthinkable. Decisions taken in the next 48 hours are critical for the whole island.