Almost 50 years ago, in the early hours of 2 February 1972, the British embassy in Dublin was gutted by fire. This was not an accident. A huge crowd had gathered in protest outside the lovely Georgian terrace in Merrion Square all through the previous day. They cheered as young men climbed across the balconies and smashed a window. They threw in some petrol and lit it. A fusillade of petrol bombs was unleashed from the crowd. People chanted the slogan they had learned from the Watts riots in Los Angeles in 1965: burn, baby, burn. The police did nothing to stop the attack. I was 14 at the time, so I wasn’t there. But some of my older friends were and I wished I had been with them. The assault was organised by the IRA, but most ordinary, peaceful Irish people approved of it. It seemed like the right thing to do, a reasonable response to the massacre the previous weekend in Derry of 13 unarmed civilians by the first battalion of the British army’s Parachute Regiment. A woman waiting for a bus in Dublin told the Irish Times: “I felt outraged that the British should do this and I felt that whatever the rights and wrongs, they would know how we felt when we burned down their embassy.” The outrage was not just the atrocity in Derry itself. It was also the way the British lied about it, falsely claiming that the paratroopers had come under fire and were protecting themselves against terrorists. The official Widgery inquiry, which essentially repeated this lie, made it clear the British state had no interest in acknowledging what had happened, let alone punishing anyone for what the Derry coroner, Major Hubert O’Neill, called “sheer unadulterated murder”. Against such imperviousness, burning down the embassy did indeed seem like the only way to let the British establishment know how most Irish people felt. Thus, 50 years after the foundation of the Irish Free State, relations between Britain and independent Ireland were about as bad as they could be. There had been other low points, particularly during the Second World War, when Ireland’s neutrality seemed, to many in Britain, a scandalous betrayal. But relations after Bloody Sunday seemed even worse because the slaughter was one episode – albeit an especially disastrous one – in a conflict in Northern Ireland that was still escalating. (1972 would indeed turn out to be the bloodiest year of the Troubles.) It felt in those months almost as if the two states on these islands were sliding uncontrollably into mutual and violent hostility. Yet, just eight days before Bloody Sunday, something completely different had happened. The British prime minister, Edward Heath, and the taoiseach, Jack Lynch, had been together in a ceremonial hall in Brussels to each sign his country’s treaties of accession to the European Economic Community. There are pictures of the two men standing shoulder to shoulder, both beaming with bonhomie. Less than a year after the burning of the embassy in Dublin, the two countries would be close partners in the European project. It is fair to say, moreover, that Ireland owed its place in what was then an exclusive club to its deep economic connection to Britain. On its own, Ireland was too poor to justify a seat at the top table of Europe. It was admitted essentially on Britain’s coat-tails. It is strange, in retrospect, how these two stories ran side by side – one of profound and deeply rooted animosity, the other of intense cooperation; one full of fracturing and division, the other a joint commitment to “ever closer union” in Europe. As it happened, membership of the EU allowed Ireland to wean itself off its dependency on the British economy and to achieve a much more substantial independence. (One of the many things Brexiters could never understand is this notion that the supposedly oppressive EU could be, for small nations, a route out of domination by bigger neighbours.) But it also became a school in which Irish and British governments learned to work very closely, and respectfully, together. That experience, in turn, made possible the joint choreography of the 1990s, the carefully calibrated steps that produced the peace agreement of 1998. By 2011, when the Queen became the first British monarch in a century to visit southern Ireland, it really felt like this good neighbourliness had become a permanent condition, that British arrogance and Irish rage were exhibits in a museum of historical curiosities. That illusion of permanence was shattered by Brexit, not just by the loss of the common ground of EU membership but also by the refusal to think at all about the consequences for the island of Ireland. Many of the Brexiters still see those consequences not as the inevitable results of their own choices, but as some kind of Irish conspiracy to thwart them. There is a corner of their minds in which Brexit would have been a rip-roaring triumph by now if the damned Irish hadn’t spoiled it with their backstops and protocols. The open attempts of the Johnson administration to tear up the agreements on the Irish dimension of Brexit have revived that old spectre, Perfidious Albion. And yet we should remember 1972. Even at that awful nadir, the stakes were far too high for Britain and Ireland to allow their relationship to deteriorate into toxicity. Two little things forced them together: history and geography. The two big islands on our archipelago can no more escape each other’s fates than Britain can float off into the Atlantic away from Europe. Maybe there are even ways in which we understand each other better. Some slow learners in Britain have discovered, after a mere century, that Ireland is an independent country with its own national interests and relationships with Europe. Irish people have discovered that they have no monopoly in these islands on identity crises and binary tribalisms. It is new for Ireland to feel like the more stable and self-confident of the states on the archipelago and new for Britain to be dealing with the fractious aftermath of a nationalist revolution. It may take some time for all of us to get used to these novelties. But in much worse circumstances, we have found ways to face new realities together. Fintan O’Toole’s most recent book is We Don’t Know Ourselves: A Personal History of Ireland Since 1958