Paramilitaries and UK armed forces were fighting in parts of the UK relatively recently and that peace is under threat by a no-deal Brexit so I'm not sure that is the best analogy.
20 years ago... that’s as long as the gap between ww2 and the summer of love
Well, the chief of the police of Northern Ireland seems to think there is an increased risk of paramilitary activity of there is a hard-Brexit causing a breakdown of the GFA:
https://www.theguardian.com/uk-news/2019/aug/22/northern-ire...
Honestly this article is a bit intellectually dishonest by saying things like "It seemed as though nothing could go wrong" in Weimar Germany in 1920. There were outright revolutions going on at that time. Like large groups of revolutionaries and freikorps machine gunning each other in the streets of Berlin within 12 months of that election. Did people back then really feel like "nothing could go wrong?"
https://www.youtube.com/watch?v=ssYACBz8gzs&t=17s