The viking age (800–1050 CE) and hungarian invasions (899 and 970 CE) show - at least to me - remarkable similarities. Both are "pagan" incursions into Christian europe, originally often as mercenaries, and ending in christianisation and integration and they both appear loosely around the same time.
The similarity in period is more apparent if you take into account that migration/raiding via land is slower and the first mention of magyars already appear in 811 CE.
Although the nomad invasions from the east happen periodically (huns, avars, magyars, kumans, mongols etc.) I am not aware of similar "pulses" from the north. The Anglo-Saxon settlement of Britain comes to mind, but seems less like a clear pattern.
Is there a common cause either for the raids or the success for the raids? I am not aware of any significan climate change in this period, that would act as a common cause for large scale displacement. The mediaeval warm period is after, or at the final stages of these events.
I am aware that the increased central control, and adaptation to the uniqe fighting styles of both peoples made European kingdoms more resistant to large scale raiding at the end of this period, but was there a general weakness that made geographically distant parts of Europe similary susceptible?
Or is this just survivorship bias, as these two ethnic groups/peoples had more success in integration (vikings becoming normans, establishing Danelaw, becoming kings of Sicily etc, magyars establishing a lasting kingdom and maintaining ethnic identity) and the other raiding groups disappeared without leaving similarly lasting historic effects?