I’ve never heard of any Welsh nationalism desending into violence until I got chatting to an Englishman in my local a few months back.

Please delete if not allowed, think it would be of some interest. It’s not Irish in anyway​.

 Talked about the north etc and he asked me had had I heard of the Welsh group know had the the Sons of Glyndwr. Here is a little copy and paste from Wikipedia. 

The group first came to prominence in 1979. In the first wave of attacks, eight English-owned holiday homes were destroyed within the space of a month. In 1980 Welsh Police carried out a series of raids in Operation Tân. Within the next ten years around 220 properties were damaged by the campaign.[1] It peaked in the late 1980s with the targeting of Conservative MPs’ homes and David Hunt, the then Welsh secretary, was a target in 1990.
Responsibility for the bombings had been taken by four separate movements: Mudiad Amddiffyn Cymru (the movement to defend Wales), Cadwyr Cymru (the keepers of Wales), Meibion Glyndŵr, and The Welsh Army for the Workers Republic (WAWR) whose attacks were on political targets in the early 1980s. However, Meibion Glyndŵr has been the only group to have had any claim to long-term success, although since the mid-1990s the group has been inactive and Welsh nationalist violence has ceased, at least on an organisational level. Letters claiming responsibility for attacks were signed “Rhys Gethin”, in homage to one of Owain Glyndŵr’s most prominent followers.
A reinvestigation into postal bombings led to the conviction of Sion Aubrey Roberts in 1993. A Plaid Cymru member of parliament, Elfyn Llwyd, speculated that the group was an MI5 front.[1]

With many thanks to: Shane Meade – All that is Irish past and present.