History casts a long shadow: most especially the history of our island. The conquest of Ireland by Britain, effected over a period of five centuries and culminating in the Williamite settlement of the late 17th century, was tragic for Ireland, but it always had the possibility of a clear-cut resolution by way of land reform and eventual acceptance by Britain of Irish independence.
Conquest, in other words, was always potentially reversible.
However, the post-Reformation settlement of much of the north-east of our island created an extraordinarily intractable problem. Religious differences blocked eventual assimilation of the settlers by indigenous Irish culture, as had in considerable measure taken place with pre-Reformation Norman and English rural settlements in Ireland.
And centuries of mutual hostility were guaranteed by the consequent irresolvable conflict between the new unassimilated settlers on the good land of Ulster and the former owners of that land; a conflict that industrialisation merely transferred to a new 19th-century urban setting.
The depth of that conflict was never fully grasped in the rest of the island, whose people never came to terms with its reality. Any chance there might have been of a gradual, very long-term, resolution of this conflict if the island had remained united was blocked by Partition.
That policy was seen in Britain as a way to head off conflict within Ireland in the short term. It was designed to extract Britain from a troublesome direct involvement in governing Ireland, while also appeasing domestic tensions in Britain itself and securing that country's strategic interests.
Its immediate effect in Ireland was to enable local majorities in both parts of the island to create uni-cultural polities within their areas. In the South the minority was prosperous and too small to appear as a threat; so, although culturally isolated, and finding itself "in a cold place", it was left free from actual discrimination and allowed to prosper economically.
In the North, however, an alienated minority, comprising initially over one-third of the population with, however, a high birth rate, appeared as a threat to the majority, a threat strongly reinforced by Southern irredentism: "Give us back our lost six counties". The fear thus generated among the majority in the North led to carefully disguised political and economic discrimination.
The unionist government succeeded in avoiding potential British pressure to end these practices by an implied (but on at least one occasion overt) threat of resignation, which would have precipitated a re-engagement of Britain in the troublesome governance of that part of the island.
This was the last thing British politicians wanted to face but, in the longer term, their deep fear of such a fate and efforts to avoid the issue over 50 years eventually served only to plunge it into a deeper and more unpleasant situation than they could ever have imagined possible.
If Britain effected the political partitioning of Ireland, it was successive Irish governments - in an understandable concern to create in their new State a climate reflective of the assumed aspirations of the vast majority of its population - which completed this process, by creating in the South a quite new cultural environment, alien to the Protestant unionist majority in Northern Ireland.
In developing a Roman Catholic ethos in the Constitution and laws of the Republic (as it eventually became) and in giving priority to the revival of a language that was alien to almost all the Protestant people of Northern Ireland, the division between North and South was greatly deepened - without any thought for the consequences for the dream of eventual Irish unity.
From these events a deeply paradoxical situation emerged on the two sides of the Border, the reality of which seems to have escaped almost everyone.
First, on the Protestant unionist side, their artificial electoral majority within the six-county area never translated itself into a psychological sense of being actually a majority. Because of decades of Southern hostility and of Northern nationalist resistance to their rule, the Protestant unionist community could never lose a sense of being a threatened minority on the island of Ireland. In that key respect, and at the deepest level - that of fear - unionists in Northern Ireland continued to think in all-Ireland terms.
In sharp contrast, the nationalist people of the rest of the island, while retaining at least a theoretical commitment to Irish unity, rapidly became deeply involved in the construction of their new State, with its own complex set of new institutions.
Within a very short period, we in this part of Ireland, for practical purposes, ceased to think of the island as our home, but came to identify primarily - one might say almost exclusively - with our new State.
There have been exceptions in the cultural sphere, of course. Most notable has been the GAA, through which, for Gaelic sports at least, the people of this part of Ireland retain a sense of being part of the whole island of Ireland.
This is true also of our churches, to a considerable degree of our trade unions, and also of some professions and other activities which were already organised on an all-island basis before Partition.
Paradoxically many of these latter are "Royal" institutions, such as the Royal Colleges of General Practitioners and of Physicians of Ireland and the Royal College of Surgeons in Ireland; the Royal Dublin Society; the Royal Hibernian Academy; the Royal Horticultural Society, Ireland; the Royal Institute of the Architects of Ireland; the Royal Irish Academy; the Royal Irish Academy of Music; and the Royal National Lifeboat Institution.
The useful role of such bodies in maintaining North-South links has, I suspect, protected them against populist pressure to drop the "royal" prefix.
But for most purposes we have come to think and act as citizens of the Irish State rather than as inhabitants of an island of Ireland.
Many on this part of the island are impatient with what they see as the negativity of many unionist actions and reactions. We are not good at empathy, at imagining how we in our turn would behave in the kind of situation in which they now find themselves.
Not having lived in the same kind of uncertainty and fear as they have done for decades past, we assume that in a situation similar to theirs, we would behave calmly and rationally. I doubt it.