The assassination of Field Marshal Sir Henry Wilson MP on June 22nd 1922 was a profoundly shocking event in British and Irish history. There had not been an assassination in Britain of a sitting MP since the prime minister Spencer Perceval who was killed in 1812.

Wilson was shot dead on the doorstep of his home at 36 Eaton Place in Belgravia by two wounded Great War veterans turned Irish nationalists Reginald Dunne and Joe O’Sullivan.

Reginald William Dunne

Wilson was elected unopposed as the Ulster Unionist MP for North Down in February 1922, but he was better known as the Chief of the Imperial General Staff (CIGS), the head of the British army.

He held that position in the final year of the First World War when a combined Allied offensive brought about the defeat of Germany and was one of the men who won the war according to many of his contemporaries.

His assassins had embarked on a suicide mission as O’Sullivan had lost a leg at Passchendaele and Dunne had been wounded in the knee and invalided out of the British army.

They were caught and interrogated. A copy of the official IRA publication, An t–Óglách, was found on Dunne. It was enough for the British Government to blame the assassination, erroneously as it turned out, on the anti-Treaty side which has rejected the peace settlement agreed between Britain and Ireland in December 1921.

The Anglo-Irish Treaty, which established what is now the Republic of Ireland, split Irish republicanism between those who accepted the Treaty and those who rejected it as a sell-out.

The IRA which fought the War of Independence wanted a wholly independent Irish republic; instead the Treaty established an Irish Free State which had Dominion status within the British Empire and retained the British monarchy as head of state.

In April 1922 anti-Treaty rebels occupied the Four Courts in Dublin in defiance of the Provisional Government. The Wilson shooting provided the pretext for the British Government to issue an ultimatum to Michael Collins – deal with the anti-Treaty rebels or we will do it for you.

The officer commanding British forces in the country, General Sir Nevil Macready was summoned to London and he found the British cabinet in a “state of suppressed agitation” and spoiling for revenge.

Winston Churchill, then the Secretary of State for the Colonies, was charged with a “feverish impetuosity”.

Macready was horrified and believed the government was walking into a trap. “The few senior officers to whom I unfolded the scheme were unanimous in their agreement that it could have but one result, the reopening of hostilities throughout Ireland.”

Joseph O’Sullivan

Four days after the Wilson shooting, Churchill told the House of Commons in public what the prime minister David Lloyd George had told Collins in private. If the Provisional Government did not deal with the rebels occupying the Four Courts, the British would consider the Treaty to be violated.

Fortunately for the British, the kidnapping of a Free State general, J.J ‘Ginger’ O’Connell, gave the Provisional Government a pretext to attack the rebels. At 3.50am on the morning of June 28th the newly established National Army shelled the Four Courts using borrowed British guns. The Irish Civil War begun. It pitted erstwhile comrades against each other and was prosecuted with a savagery which scarred the first Irish state in history for generations.

Ironically, the Wilson shooting had nothing to do with the Treaty and everything to do with the sectarian violence in Northern Ireland which began in the summer of 1920 and led to a number of high-profile massacres of Belfast’s Catholic minority population.

Wilson was appointed military adviser to Sir James Craig’s Northern government in March 1922. As such he was blamed by nationalists for the introduction of the Special Powers Act and for the actions of the Ulster Special Constabulary (USC).

Wilson was a southern unionist from Co Longford and yet an uncompromising foe of Irish nationalism. He believed the Anglo-Irish Treaty was a sell out to what he called the “murder gang”.

He fell out with Lloyd George who trusted his judgement in the First World War, but could not abide his contrarian views on Ireland.

Wilson was an Irish-born British imperialist killed by two British-born Irish nationalists.  Dunne and O’Sullivan were hanged for murder on August 10th, 1922. They went to the scaffold believing they had done the right thing.

At his trial Dunne told his jurors: “I wish to state that if, as I surmise, you will find me guilty, although some of you may have been my comrades in the late war, I trust that a higher court, the only court that matters will judge me by my actions in this world and consider the purity of my intentions.”

Ronan McGreevy is an Irish Times journalist and author and the author of Great Hatred: The Assassination of Field Marshal Sir Henry Wilson MP is published by Faber & Faber.

Aspects of History Issue 9 is out now.