this you'll have to clarify, because it's a very strange statement
the U.S. has been fighting somewhere or another - or usually multiple somewheres - forever
As you say, the US has been fighting somewhere or other - or usually multiple somewheres - forever. Therefore a long-term, disciplined military campaign IS the history of the US. I don’t see a contradiction there.
The IRA was an amalgamation of multiple world views united under the ideology of the free state. What that free state would look like had as many interpretations as there were interpreters. The provos operated differently during the Troubles to the IRA of the early 20th century. The longer history of the island means comparisons with the US aren’t really helpful and probably hinder this debate. In the late first/early 2nd millennium AD Ireland was invaded by the Norse, the Normans, plunged into power vacuums by events like the flight of the earls, then that cunt Cromwell, the plantations in the north, the famine etc. These mirror some of the experiences of Britain in the first millennium AD - invasions by Romans, Anglo-Saxons, Norse and Normans etc, but v different dynamics too.
The extreme right in the US bleeds into milder conservative world views because of nationalism. The flag is the central default spoke in their wheel that unites them. Are these ‘types‘ capable of more organised campaigns of violence? Absolutely, but the Irish analogy really doesn’t help. They’re completely different worlds. So much depends on the forthcoming election. It could enable or disable momentum. So many weapons in the hands of idiots with sketchy intentions is never good.