The right of people in Northern Ireland to identify as either Irish or British is enshrined in the Good Friday Agreement.
It is a cornerstone of the peace deal after three decades of conflict.
This was a breakthrough because identity politics really matters in this part of the British Isles. Identity was a significant part of the Troubles - republicans fighting to be Irish and loyalists fighting to stay British - and it cost more than 3,500 lives.
Letting people choose rather than impose an identity meant both sides of the divide could, to some extent, regard themselves as the ‘winners’ of the conflict.
This solution was not perfect, and it required a certain amount of imagination, but by and large it has worked. A fragile and imperfect peace prevailed under this arrangement.
For this to work in practice, it helped greatly that borders between Northern Ireland, the Republic of Ireland, and mainland Great Britain have been kept completely invisible. Hard border infrastructure would rather spoil the illusion.
Of course, the Good Friday Agreement was drafted long before Brexit in its current form was even a twinkle in Prime Minister Boris Johnson’s eye.
Now, the UK Government has now conceded there must be some kind of border as a consequence of Brexit, the only question is where it goes.
And that is a significant problem. Wherever you place a hard border, it meddles with the identity of people in Northern Ireland.
- Jim Wilson, an east Belfast loyalist community worker, says the DUP has been 'dumped on' by Boris Johnson
Put it on the land and you are creating a barrier between Belfast and Dublin - you push those who call themselves Irish in Northern Ireland further away from their Irish identity and closer to being British.
Put it in the sea, as is being proposed by the PM now, and you create a barrier between Belfast and London - pushing those who identify as British further away from their British identity and closer to being Irish.
The prospect of a land border drew threats of violence from Irish republicans.
Both the UK and the EU were acutely aware of the sensitivities around this, and pledged to avoid it (a rare early agreement between them).
The so-called Sea Border is seen as the most practical solution because the water forms a natural ‘hard border’ and port infrastructure is already in place to carry out checks.
It is, however, important to remember there were two sides in the conflict here.
Putting the border between Northern Ireland and the rest of the UK upsets the loyalist community who identify as fiercely British.
They see this as a bigger step toward a United Ireland than anything the IRA achieved through bullets and bombs. And they’re calling, in blunt terms, an act of betrayal by the British government.
- A 'can of worms' has been opened up by Johnson's Brexit deal
We are talking about a community that spilled blood to keep Northern Ireland in the UK, and now they believe Westminster is prepared to hand them over as though they were the price of securing a British Brexit.
They are also astonished that, in their eyes, republican threats of violence have been rewarded and wonder if they have been punished for not doing the same.
To be absolutely clear, loyalists are not openly threatening violence. They are angry, they feel cheated, and there are reports they’re trying to organise themselves to make their opposition to this deal clear.
Those I have spoken to in the loyalist community say they want to avoid conflict or any kind of protest that breaks the law - hundreds of young loyalists have criminal records from previous high-profile demonstrations and the leaders want to steer well clear of that.
They hope a political solution can be found. They also think it’s a test for their community - if they don’t give pushback, or they are unable to organise themselves in any meaningful way, then it raises serious questions about what level of influence they really command in modern day Northern Ireland and whether they should be listened to at all on future key issues in this little country.
It is also important to point out the loyalist community is not speaking for the whole of Northern Ireland.
This is a nation voted overwhelmingly to Remain in the EU. The early signs are most people here are quite receptive to this deal because it keeps them closely aligned with the EU, while also keeping the benefits of being in the UK.
However, the debate around Brexit has started to pick away at scabs from Northern Ireland’s old wounds.
It took a lot for these to heal, and no politician - in the UK, Ireland, or the EU - should expect to tamper with that without consequence.