Decision to spare Dev's life changed the face of political life forever
The recent RTE drama Rebellion featured a scene in which Eamon de Valera and other 1916 Volunteers are about to be shot by firing squad. At the very last minute, a British army officer tells them that their sentence has been commuted to life imprisonment.
The future Taoiseach and President is so relieved that he immediately doubles over and vomits - much to the disgust of his fellow revolutionaries.
As de Valera's grandson Eamon O Cuiv has complained, it did not happen quite like that. Even so, this reprieve was an absolutely critical moment in the political history of Ireland.
Dev and the other 1916 survivors went on to fundamentally shape the party system we have today - one still largely intact even despite last month's seismic general election.
The Rising featured many people who would become seminal names in Irish politics. The most glamorous was Michael Collins, revered today as Fine Gael's spiritual leader, even though he died before it was founded.
W.T. Cosgrave and Desmond FitzGerald served as President of the Executive Council and Foreign Minister in the first Free State government - and both had sons who ended up in the Taoiseach's office.
On the Fianna Fail side future President Sean T O'Kelly and future Taoiseach Sean Lemass fought together in the GPO, while Lemass's son-in-law Charles Haughey also made it to the top. As for Labour, they could boast that James Connolly founded their party in 1912.
It all started, however, with de Valera. The only 1916 commandant to escape execution (for reasons that historians still dispute) suddenly enjoyed an iconic status within Irish republicanism.
The Sinn Fein founder Arthur Griffith, who had not fought in the Rising, recognised this and handed the leadership over to him at the party's 1917 Ard Fheis.
When a general election came around in 1918, Dev made a critical move. He persuaded Labour that freedom had to be achieved before socialism, which meant standing aside and giving Sinn Fein a clear shot at the Home Rule Party.
Dev's troops duly won the election, giving conservative nationalists a big head-start over left-wing nationalists - one that they are still clinging onto almost a century later.
To put it another way, Patrick Pearse's Gaelic vision had won out over James Connolly's social radicalism.
This is still the main reason why Ireland, unlike every other country in Europe, has never had an openly left-wing government.
When asked about this, de Valera famously declared, "Labour must wait" - and last month's election drubbing will force them to wait for at least a bit longer.
After 1918, the War of Independence, Anglo-Irish Treaty and Civil War split Irish nationalism into several different factions. The pro-Treaty side took power as Cumman na nGaedheal and later morphed into Fine Gael. De Valera soon decided that he was willing to compromise for power after all and set up his own Fianna Fail party in 1926. The remnants of Sinn Fein faded away and were irrelevant to southern politics for 70 years.
Before long, a pattern emerged at Leinster House. Fianna Fail and Fine Gael alternated power between them, with Labour occasionally drafted in to make up the numbers.
Irish politics was a 'two and a half-party' system, without any traditional left-right divide - with the bonus that fascism and communism never got a look-in.
With so many Easter Rising veterans in Dail Eireann, the event itself cast a long shadow.
"Where were you in 1916?" and similar insults were common during Dail debates.
As late as 1948, Fine Gael leader Richard Mulcahy was denied his chance to become Taoiseach because he had ordered the executions of so many republican prisoners during the Civil War.
Over the years, new political players such as Clann na Poblachta, the Progressive Democrats and the Green Party have all tried to break the 1916 mould.
All of them have either gone bust or been quickly reduced to tiny numbers.
Even in last month's historically fractured election, 70pc of voters still supported parties who claim at least some link with the Easter Rising.
So how would Irish politics be different if the British had decided to shoot de Valera after all? Like so many other debates about 1916, we will simply never know.