I have just seen a very disturbing documentary on BBC TV. It concerns the allegations of atrocities made against the German Army by the Allies in WW1. These included an allegation that a Canadian sergeant was crucified with bayonets near Ypres in 1915, stories of babies being bayonetted, rape of women, and mass executions of civilians.
In 1919, the German Government not unreasonably asked the British to "put up or shut up" and the British and Canadian Governments carried out enquiries, which failed to find the evidence.
The upshot was, of course, terrible, in that in WW2 no-one was willing to believe the absolutely true accounts of what the SS were doing, thinking that these were also "made up" atrocity stories. Massacring people just because they were Jews? Absurd!
The disturbing aspect of the programme was that modern research has shown that the horror stories were true. A baby was bayonetted, and a Canadian sergeant was crucified near Ypres. There were mass executions of civilians in Belguim in the firts weeks of the war. These seem to have been caused by what we now recognise as "friendly fire", attributed then by the German (constcript) Army to fire by civilian "francs-tireurs".
Pretty worrying stuff - not in relation to Germany, but in relation to all sorts of other rumours. One concludes that they often have a basis in fact.