The problem of a united Ireland is that all sides - republicans, unionists, the neutral of North and Republic, the British - envisage this as the subsuming of the North's six counties into the southern state.

This is never going to work. What *would* work, and what *will* work is when the North and the Republic join as equal partners, and move gradually into co-operation in a state that subsumes both entities into a shared and new Ireland.