It's hard to credit, given the sad and forlorn state of today's Ulster Unionist Party, that it was once in sole charge in Belfast, given a free hand by Westminster to run Northern Ireland pretty much as it wanted.
In the 1920s, a Home Secretary wrote to James Craig, leader of the UUP and Northern Ireland's first prime minister, to assure him that: "I know my place and don't propose to interfere." That set the tone for half-a-century of unionist party rule.
Given such leeway, Craig and his successors opted for the politics of the fortress, consciously building an extremely static society. Suspicious of the Catholic minority, the south and, of course, the IRA, they set their face against any notion of inclusion.
Their party fossilised in terms of both attitudes and personnel. Craig was prime minister for 19 years, while one of his successors, Lord Brookeborough, held the post for 20. By 1939, Craig and four of his seven ministers had been in the cabinet for 18 years.
Politically, this was no country for young men. But the 1960s brought winds of change to many parts of the Western world, as figures like John F Kennedy and Harold Wilson stressed youth and modernisation.
Terence O'Neill – only the fourth Unionist prime minister in 40 years – was no dangerous radical, advocating modest reforms in an effort to keep up with the rest of the world.
But while he thought of this as no more than political and economic common sense, the first open, serious splits within unionism developed: a substantial section of Protestants viewed even limited change with the deepest suspicion.
This produced a number of unionist dissidents, most notably in the formidable figure of the Rev Ian Paisley, who tormented O'Neill and his successors as unionist leader.
With the DUP and other groupings emerging as significant forces, unionism was never again referred to as a monolith.
With the sense of unionist unity gone, the reality of unionist power also disappeared when Westminster shut down Stormont in 1972.
That happened after Brian Faulkner failed to convince Edward Heath that he could deal with fast-rising violence and increasing polarisation.
For decades afterwards the once-mighty party remained the largest political grouping, but lost virtually all political power.
Faulkner made a short-lived comeback in 1974, transforming himself from a hardliner to a powersharer, but was brought down by the UWC strike.
That stoppage demonstrated that unionism could flex its muscles and could veto attempts to include nationalists in government.
But it also demonstrated that it could not compel London to bring back Stormont.
Then a new philosophy emerged under the leadership of James Molyneaux, who headed the party from 1979 to 1995.
Instead of pressing for a revived Stormont, which he rightly calculated would only come about with power-sharing, he settled for making the best of the status quo, direct rule.
He once quite proudly spoke of himself as a general who "has the satisfaction of repulsing all attacks on the citadel". In some ways this worked: he did well, for example, in holding off the threat to his party from the DUP.
But the world moved on around the unionist party with the turbulence of events such as the 1981 hunger strikes, the 1985 Anglo-Irish Agreement and the 1994 IRA ceasefire. Molyneaux was eventually deposed, reasonably politely but certainly firmly, from the leadership, with David Trimble assuming the mantle for what would prove a particularly turbulent decade.
It was a time of negotiation, uncertainty, many changes of mind and above all of splits and fracturing: remember all those party meetings aimed at defeating Trimble?
By the end of Trimble's 10 years votes had drained away from the UUP to the DUP, with many seats lost and the DUP gaining important defectors, such as Arlene Foster and Jeffrey Donaldson.
The loss of UUP support accelerated after 2007, when Paisley became first minister, a bold move which was one of a number in which he tactically outmanoeuvred the UUP.
Since then, it is hardly unfair to say, the UUP has floundered under Reg Empey, Tom Elliott and now Mike Nesbitt. Empey's tactic of linking up with the Conservatives failed to stop the slide; Elliott baled out complaining of "obstruction and hostility";
Nesbitt's efforts to impose discipline and purpose have brought more defections.
Basically, the Ulster Unionist Party has proved itself unable to win friends and influence people, or indeed to produce popular new policies or approaches, since the 1970s.
Faulkner and Trimble were given chances to make a new start and tried manfully to do so, but neither succeeded.
Unionism's one-party control during the half-century of Stormont's existence haunted it for decades, in that it stuck to the politics of exclusion and did not display competence.
When times changed, from the mid-1990s on, it was prepared to consider departures from tradition.
But, by that time, it was too late; the DUP had adapted much better to the changing times. The UUP, which had not managed to carve out a clear identity and a clear sense of purpose, has wound up in its present, deep difficulties.