Flux is the permanent state of human affairs: Empires rise and fall, despots come and go, alliances are built only to fall apart, social norms once thought inviolable are thrown aside.
Every now and then, we inflict catastrophic harm on each other. Sometimes, that harm is so visceral, so in-the-marrow, that we try to overcome differences, so it might not be repeated.
Twice, in the last century, we plunged those depths. Three great alliances are legacies of those calamities.
The United Nations was established in October 1945, almost hours after the Second World War’s guns fell silent after six years of carnage.
The objective was, and is, to maintain international peace. Ireland contributes to that process.
The UN, like any organisation of that scale and ambition, is not beyond reproach, but it remains a vital, if stressed, cog in international geopolitics.
The European Union is another child of the last century’s catastrophes. That great project sustains an unprecedented peace.
Like the UN, it is far from perfect and, as President Michael D Higgins argued so convincingly recently, it needs to refocus and reform to recover its core values and truths.
He expressed hopes earlier articulated by France’s president, Emmanuel Macron, even if the two men might disagree — slightly — on how the EU might be rejuvenated.
Despite the tragedy of Brexit, that urgent objective is attainable. Next month’s European elections will be part of that process.
The North Atlantic Treaty Organization is the third leg, the military one, of that three-legged stool.
Established as an intergovernmental military alliance between 29 North American and European countries, it was founded 70 years ago this week.
One of the events planned to mark that milestone will be a visit to the White House by Nato secretary-general Jens Stoltenberg tomorrow.
Mr Stoltenberg hopes to rebuild a relationship strained last year when Mr Trump, flux personified, threatened to pull out of the military alliance.
Mr Trump, so very dramatically, but to no comprehensible end, threw Nato’s summit in disarray by threatening to walk away from the alliance.
His behaviour, so quickly following his impetuousness at the G7 summit in Canada, underlined the growing tensions in the West and cannot have gone unnoticed among the ever-circling opportunists — as the inevitable ignominies and draining-away of solidarity created by Brexit are, too.
But what relevance is Nato’s 70th birthday to Ireland?
After all, we are neutral; we are not in the club. However, we are happy to bask in the reflected stability and prosperity the organisation guarantees.
We, like the Brextremists, want to have our cake and eat it.
Any suggestion that our neutrality is, at best, a dishonest evasion in today’s fragmenting world is rejected as forcefully as any questions around Cathleen Ní Houlihan’s chastity.
It is not hard to argue that our neutrality is a legacy from a time when not being neutral meant supporting one British adventure or another.
That is no longer the case. Times — and the threats we face— have changed.
Our neutrality looks ever more like an indulgence than a noble principle.
Times change; maybe we should, too.