As the Ulster Unionist Council meets in Belfast this morning, its members are once again called upon to raise their eyes from the distasteful compromises they have reluctantly made, to the bigger picture painted by the hand of history invoked by the Prime Minister.

As the Ulster Unionist Council meets in Belfast this morning, its members are once again called upon to raise their eyes from the distasteful compromises they have reluctantly made, to the bigger picture painted by the hand of history invoked by the Prime Minister.

Nor should they focus only on the history of these islands. The collapse of the Israeli-Palestinian talks is a grim reminder that peace processes need more than simple momentum to keep them going. In Israel as in Ireland, the fact that the broad outlines of a settlement are obvious is no guarantee that agreement can be reached and sustained. In Israel, the settlement includes a self-governing Palestinian state, with a limited right to return for refugees and some kind of shared control of Jerusalem. In Ireland, the settlement is already in place, with Mark Durkan's budget, welcomed on all sides, a landmark in the normalisation of power-sharing politics.

Neither in Israel nor in Ireland, however, is the path of peace a straight line, travelling predictably from conflict to contented, dull normality. It is all too easy for leaders, carried on the shoulders of world opinion, to forget that peace agreements need to be underpinned by concrete and consistent benefits to their followers on the ground, who will otherwise be attracted by the rhetoric of extremists. And extremists, such as Hamas and the so-called Real IRA, tend to become more active the closer leaders come to a solution. Equally, though, the fact that a process of conflict resolution sometimes goes backwards does not mean that the underlying desire for peace has weakened.

The compelling reason for Unionists to continue to support the Good Friday Agreement remains the same now as when it was endorsed by the people of Northern Ireland, including a bare majority of Unionists, in the 1998 referendum. It is that there is more chance of republican disarmament under a devolved government in Stormont than under direct rule from London.

That is the overwhelming reason why Unionists should vote to support David Trimble today, and it is why yesterday's Belfast Telegraph opinion poll found that most of the party's voters want them to do so. It is no use those who have always opposed the Good Friday Agreement, or even those, like Jeffrey Donaldson, who have sometimes opposed it, complaining that the IRA has not yielded a single gun or ounce of Semtex. Almost the whole point of the Agreement was that it did not make weapons decommissioning a condition of Sinn Fein's entry into government. But that is not to say that Unionists have gained nothing from it. The IRA has gone much further in putting its weapons "beyond use" than anyone ever thought possible. The Republic of Ireland has renounced its territorial claim on the North, and Sinn Fein has accepted the right of the people of Northern Ireland (rather than of the island of Ireland as a whole) to determine their own future.

None of this is enough for Unionists whose stomachs have been turned, understandably enough, by the sight of convicted IRA killers let out of jail free and of Martin McGuinness, a reformed terrorist, in a ministerial car. But they cannot afford to be fastidious now. If the positive arguments for supporting Mr Trimble are not enough, let them consider the negative example of the Middle East.