A bit of history - in Northern Ireland, before the Good Friday Agreement, the IRA was killing MPs...

Part of that was because they didn't feel they had a representation. So now they do have a lot more self-government, including a Northern Ireland Assembly and Northern Ireland Executive. They to some extent are a state within a state already, and if they close the border with Ireland, that agreement is broken... I'm sure you already have some of the IRA gearing up.