How the idea of stripping citizenship for crimes spread across Europe

Also they're suspiciously silent about WHICH treason led to this idea spreading most recently: joining Daesh, and torturing people in Syria/Iraq, then getting left behind in camps when the state collapsed or just abandoned (sometimes/in sad cases with kids) when divorced (obviously for women). Does "terrorism" without clarification really cover this case?

https://en.wikipedia.org/wiki/Shamima_Begum

"The Daily Telegraph reported that Begum had been an "enforcer" in ISIS's "morality police", and had tried to recruit other young women to join the jihadist group.[20] The report said that she was allowed to carry a Kalashnikov rifle and earned a reputation as a strict enforcer of IS's laws, such as dress codes for women. An anti-IS activist was also reported by The Daily Telegraph as saying that there were allegations of Begum stitching suicide bombs into explosive vests so they could not be removed without detonating.[21] None of this was proved, and much of what has been reported in media is denied by Shamima Begum."

Even in that case, the vast majority of these people were allowed to return. In bad cases they lost their kids, or were forced to do a few years in prison. But in cases where they were screaming in western courts that they wanted to behead every last Yezidi and "feed their meat to the dogs" ... yes, in that cases citizenship was removed.

So I think it's pretty fair to say I don't think we're anywhere close to the point where the slope gets slippery yet.

Also ... there is a LOT of evidence that this did in fact deter people from joining foreign terrorist organizations and massacring innocents in the middle east.