How about :
As de Valera, now in the opposition, starts calling in 1948 for an end to the partition so as to get some electoral pull, the Government/Parliament of Northern Ireland already incensed by de Valera's neutralist stance during WW2 supports raids by Orangist extremists over the border. As the IRA retaliates with a campaign of bombings, prominent Orangists claim the population of Northern Ireland now needs a buffer zone to be established further south. London, aghast at the proposal, tries to bring back Orangists and Republicans to the negotiating table, but by that time it's too late for holding talks.
The RUC, helped by various Orangist militias, start clashing with Garda units in Eire, prompting the Irish Army to deploy along the border in the Fall of 1948. The IRA/PIRA naturally fan the flames of the conflict, possibly launching "deniable" raids against targets both in the South and in Ulster to weaken moderates from both sides. Their reasoning is that, even if the UK is forced to intervene on behalf of the Orangists, the result will be a radicalization of Irish Catholics.
With the Irish Army moving into the Six Counties, and unrest in the North Irish Brigade regiments, the Attlee government decides to step in in mid-October. That move is partially based on a MI-6 report stating the Eire aims at complete annexation of Ulster. In the late 1950s, it will be discovered that the report was written by members of the spy ring set up by Harold St John Philby, MI-6 liaison officer to Washington, and that it was little but slightly modernized quotes of Republican speeches from the 1916-1921 period.
In late October, British troops slated for a deployment in Germany are re-routed to Ulster as pre-existing war plans are rapidly updated. The bombardment of Eire cities to cut Republican supply lines is discussed, but shelved away as the British government feels confident the superior numbers, matériel and experience of the British Army will prevail. Instead, a series of limited landings will take place to seize Republican depots and cut off their over-stretched units.
In late November, the British forces start moving south, engaging the Irish Army in a series of battles that rapidly push the Republican forces back to the partition line and then beyond. The Irish Army begins a rapid retreat made all the more murderous by the complete air superiority of British forces - while no bombing are allowed in or around cities, fighter-bombers have a field day attacking Eire soldiers in open fields. Resorting to guerilla tactics, IRA irregulars harass British forces with mines and snipers. Loyalist militias moving in the wake of the British Army to "secure the rear echelon" commit a series of murders that gain the attention of the world press, and that British newspapers are prompt to publish.
From October to December, Eamon de Valera tours America, as Eire's self-appointed extraordinary ambassador. The supports he garners from Irish-American citizens (including the recently-elected Massachusetts's Congressman John Kennedy) is multiplied by two factors :
- distrust for Attlee's socialist leanings among the Truman Administration, and
- the necessity to bring a quick end to the Irish crisis when threats criss-cross the board, from China and India to Israel and Berlin. Some Hawks amongst the US Administration (and in the Republican Party) accuse the UK of having aggravated the Berlin crisis by canceling the deployment of troops in Germany, and sending the wrong signal to the USSR by diverting troops and airlift capacity from Germany to Ireland.
The streets of Belfast turn into a battlefield, as pro- and anti-intervention organize mass marches and protests, and more often than not clash with each other. Still, egged by the Northern Ireland government, the British Cabinet reiterates its intention to drive all the way to Dublin and force a complete surrender of Eire, after which a negotiated settlement of the partition will come. While Attlee probably meant a return to the status quo ante, Orangists and Republicans understand it as Britain willing to push the border further south.
In early 1949, Truman finds himself and the whole Western alliance into a corner. Communist forces are gaining ground in China and French Indochina, and tensions flare up along the South Korean border. In Europe, tensions are at an all-time high over the status of Berlin. Britain's Irish adventures tie up an increasing number of troops, and limit Operation Plainfare's efficiency as British transport planes are needed elsewhere. Feeling that he has to force the decision somewhere or lose everywhere, Truman demands an immediate lift of the blockade over Berlin, and adds that America will not stand idle when a city of millions is taken hostages and the security of thousands of Allied troops is threatened. In a message to Attlee, he also underlines that the extent to which America will be able, or even willing, to help defend Britain will depend upon Attlee's decisions regarding Ireland.
Stalin, knowing the Soviet conventional superiority is threatened by the US deployment of atomic bombs, also reckons it's now or never. On March the 15th, 1949, the world enters its third world war.
WW3 starts with the annihilation of Allied forces in Berlin. An attempt to break Berlin's encirclement fails in the face of superior Russian forces. A series of bloody urban battles ensue in the former German capital, as British, American and French forces find themselves forced to repel Russian assaults on their positions.
While Berlin burns again, Russian forces make a run for the Rhine, driving deep into the British Occupation zone and seeking to cut off the lead British elements in a "run for the North Sea" offensive. In the South, French and American forces are clobbered in Bavaria, and cannot join up with their forces in West Austria. France and Great Britain order the general mobilization, and start pulling forces out of Asia to beef up their defenses.
In Ireland, the break out of WW3 brings a full stop to the British offensive, which stops in its tracks thirty miles north of Dublin. The Irish government declares itself neutral in the crisis - but calls upon the Great Powers to defend its invaded territory. Hard pressed in Bavaria, the US Administration demands, and obtains, that British forces currently in Ireland are immediately redeployed in Belgium and France, before the Russians can break the line of defense along the Ruhr. The newly-created USAF was the service least affected by demobilization that had followed WW2, and therefore was thrown into the cauldron as a last-ditch reserve. From bases in France and England, squadrons of B-29 started obliterating Russian infrastructure in Ukraine and Byelorussia. Atomic bombs were used twice against Soviet concentrations in Germany, and three more times against targets in Russia itself. In return, Russian bombers firebombed London, Brussels and Paris, as well as US forces in Japan.
In April the 4th, not a single British soldier remains in Ireland - and two of the North Irish Brigade regiments have been sent to Germany as well. After a series of Orangist/IRA murders, the remaining units of Eire move north again, first to re-establish its authority over counties lost to the British offensive, and then, once again, they cross the partition line. The Eire Taoiseach gives assurances to Truman that the move does not and will not constitute an annexation, but aims only at protecting Irish Catholics in Ulster and to disarm both Orangist militias and IRA cells. To make the move more palatable to Truman, the Eire government offers the US a military alliance, making Eire an ally in the war and therefore the Republican forces moving into Ulster a simple relief of duty of Allied troops.
For the duration of the war, Ireland is run by a joint Eire-UK commission, with police forces made up of Garda and RUC units.
WW3 ended as brutally as it had started. Soviet forces had started crossing the Rhine and pouring into the Po valley in force in the Fall of 1949, when Josef Stalin died, officially of a stroke. Three days later, it was announced that Lavrenti Beria, the head of the dreaded KGB, was stepping in.
By that time, most of Western Europe, and most of Western Russia laid in ruins, either from ground battles or from heavy air bombing. In August, 1949, Soviet Tupolev-4s bombed Belfast and Manchester. The raid on Northern Ireland, largely covered by Irish and British papers, prompted a show of solidarity from all over the island. Almost overnight, the men of Belfast had ceased to be seen by Dubliners as the worst enemies of the Republic, and started to be referred to as "our stricken brethren up North".
Upon seizing power, Lavrenti Beria made peace offers to the Western nations. He was anxious to avoid further nuclear bombings that the SU could not retaliate to in kind, and was eager to use the Soviet's early success in Europe as a bargaining chip before the situation grew any worse. On the 12th of November, 1949, it was agreed that Germany would be "Finlandized", remained a demilitarized, neutral territory separating the two blocs. While most of Western Europe had been safeguarded, the European colonial empires immediately started to crumble as the Home nations found themselves lacking the troops, or the funds, necessary to maintain their position in Asia and Africa.
In 1950, the US Administration monitored an island-wide referendum in Ireland, which gave a short but meaningful majority in favor of an end to the partition. In what was called the Shannon Agreement, Ulster was to be granted by Dublin the same kind of autonomy the UK had granted it, with its own Parliament and Government. While at first elated at the prospect, the IRA leadership soon found out that public support for its actions was rapidly waning. Deprived of its cause célèbre, a UK-controlled Ulster, the IRA soon degenerated into a purely Communist-inspired movement, that the Republic of Ireland fought beak and claws into the 1990s. By that time ideologies had ceased to matter with the final collapse of the Soviet Union in 1989, and the IRA had become little more than a group of thugs.
In 1996, another referendum was held at the initiative of the Taoiseach about a vast institutional reform of the Republic. The proposed reforms planned to create three strong local governments based upon the German Länder, and more importantly to give all Irishmen equal rights, meaning an end to the Shannon Agreement. This time, two Irishmen out of three voiced their support. For the first time many Irishmen and women could remember, not only could a Dubliner stand on equal footing with a Belfaster, but both were willing to. It has taken two wars, and three quarters of a century, to finally erode the "partition mindset" that had plagued Ireland.