I'm from Northern Ireland. Back in 1916 there was a terrorist attack called the "Easter Rising", which happened in Dublin. Native Irish people who wanted the English out of Ireland took over a Post Office and tried to declare a Republic. The British army had a huge garrison in Dublin at the time, including warships, which joined in the fight.
The English rounded all the survivors and conspirators of it, and had a choice of what to do with them.
Now, the Easter Rising was really unpopular to the local people, and right across Ireland, because of the amount of death and destruction it caused in vain:
There was considerable hostility towards the Volunteers in some parts of the city. When occupying positions in the South Dublin Union and Jacob's factory, the rebels got involved in physical confrontations with civilians trying to prevent them from taking over the buildings. The Volunteers′ shooting and clubbing of civilians made them extremely unpopular in these localities.[93] There was outright hostility to the Volunteers from the "separation women", (so-called because they were paid "Separation Money" by the British government) who had husbands and son fighting in the British Army in World War I, and among unionists.[94] Supporters of the Irish Parliamentary Party also felt the rebellion was a betrayal of their party.[95]
(The Irish Parlimentary party was the MAJOR Republican party of the time, and they didn't even support the movement! Showing how unpopular and fringe extremist these guys were.)
Everyone thought they were dicks. No one supported their paramilitary efforts, and their actions during the rebellion actually made many people revile them. The British were in no danger of more attacks, no one supported the rebels.
So naturally the British had them all summarily executed, including a guy who was so wounded he had to be strapped to a chair in front of the firing squad. This did not go down well. This did not go down well at all. People were shocked at British brutality so much that the result was a massive boom to the number of people wanting to join Sein Fein (a fledgling, militant political organisation) and the IRA.
However, opinion dramatically shifted to the rebels' side in the next two years. Initially, this was caused by the revulsion over the summary executions of 16 leaders?some of whom, such as James Connolly, who was too weak to stand from wounds sustained in the fighting?and of other people thought complicit in the rebellion. As one observer described, "the drawn-out process of executing the leaders of the rising, it was like watching blood seep from behind a closed door."
Their support then gave those two extremist organisations the power to become the main forces behind Republicanism. Que almost 100 years of violence culminating in a 30 year all out balls-to-the-wall Civil war, that only stopped when both sides realised they couldn't murder everyone who opposed them, and that the British named 'The Troubles' because, like Tom Cruise, they can't handle the truth.
Today Northern Ireland is a mess. We're completely socially divided, there are still paramilitary groups on both sides that wield massive power and influence, and it honestly would not take much to plunge us right back in to war. If the British had
not killed the leaders of the Easter Rising then virtually none of that would have happened. Sinn Fein wouldn't have gained it's influence, the IRA would have remained a small fringe group, and although there would almost certainly have still been strife over the occupation, my country would be 100 times better off and
thousands of people that lost there lives in our petty land squabbles would still be alive today.