I know that there was a separate Irish Parliament up to 1801, but subject to the British Parliament’s laws. Than in 1800 the British Parliament abolished the Irish Parliament and merged Ireland into the United Kingdom of Great Britain and Ireland.
Why? was it concerns about Irish sympathies with the French Revolution, after the failed French attempted invasion of Ireland in 1798?
The Wikipedia article seems to have some details:
The Irish parliament voted in favor of a union after having been strongly against one, after some serious political machinations (read heavy bribery).
The 1798 attempted invasion was what reignited efforts to get a union in place.
One benefit would be that the vote , or will , of the people of Ireland wouldn’t be enough to become independent, it was in the UK and so any war would be a civil war, not a war of independence from a distant colonising power. This might have mattered politically, eg for the discussion of politics with continental powers… they might ask "How can you survive militarily ? Aren’t you overstretched ? how many of your colonies are revolting against your domination ? " . Well this shifted Ireland from colony to integrated territory…so didn’t count as a liability, a weakness… So the events in europe, the need to appear to be a successful power militarily and in terms of colonies, may have inspired the change.
And naybe London decided that the granting of self-determination (their own parliament, independent of London … ) emboldened the pro-independents, and so reacted to that. France had gone through a revolution, and USA had independence, so they needed to change tack ?
The politics would be that if the independent parliament of Ireland voted to join the UK , then that would have to be given time to stabilise, the people would perhaps be content with accepting it. The timing had to be soon, as the people had been given, or at least promised ?, non-discriminatory voting and parliamentary rights, eg Catholics could vote and become members of the parliament… ? or wanted it ? It was also a good time politically, because of the booming economy … mostly due to trade between Ireland and England, right ? and a share of the profits of the industrial revolution and so on, … and because they could always say they had to do it due to France, the evolution, and Napoleon…