With the exception of Gwyn Alf William's groundbreaking book, somehow this epochal moment in working class history has been overlooked outside of Wales. This is especially strange given the Peterloo Massacre and deportation of the Tolpuddle Martyrs in the same period are widely known.
My contention is that this is because of the insurrectionary nature of the rising that saw workers disarming soldiers, even liberal historians can feel at ease with the Tolpuddle Martyrs. And also that Wales has been peripheral to the vision of many English socialist historians.
The second point is more telling IMO, and an interesting admission from yourself Udo - its a clear example why a number of us find it very galling to be lectured on internationalism, and the apparently poisonous nature of any form of welsh nationalism, when many on the English left have ignored Wales and its history quite so blatantly.
Quoting Thompson is particularly striking in this context - 'Making of the English Working Class', indeed. The Merthyr Rising was never discussed or even mentioned in the several years I spent in or around the far left in England.
Commune is overcooking it (it lasted 4 days, and vapourised strangely at its height) but it is a great book. Williams really injects analysis and life into it all, particularly vivid in my memory is the workers loading stolen muskets with marbles after they ran out of ammunition, during the battle outside the Castle Hotel.
If you are ever fortunate enough to find yourself in Merthyr (

), there is a plaque to Penderyn on the of the old Library in the High Street, with a statue of S.O. Davies in front, while we are talking about lefties.
Cyfarthfa Castle, home of the 'Iron Master' Crawshay has a museum that looks at merthyr's radical history. Remnants of the foundries are also being uncovered slowly. Also at Vaynor church (between Trefechan and Pontsticill) you will see the gravestone of another Crawshay, which has a ten ton slab over it, with 'God Forgive Me' inscribed across it.
Its worth an afternoon if you are that way inclined, and passing through. You could even have a pint in the Three Horsehoes (unless its closed recently) by the Fire Station, where the Chartists used to plot. Merthyr has had a very strong local history scene for many years, and so plenty of stuff should be fairly easily available.