The annual march in which loyalists celebrate their ties to the United Kingdom comes as Brexit has created a new border in the Irish Sea — and the future of the U.K. is tenuous.

When the Democratic Unionist party decided to support Brexit, many warned that the decision could have profound consequences for Northern Ireland’s position within the UK.

As some say the call for a border poll on a United Ireland is growing, what would it take to get to that point, and what would it mean to be a Unionist, if the Union no longer exists?