If you think the US is the only one that has looney Sovereign citizens. Germany has its own movement at its even crazier.
Basically, Reichsbürger translated means ''citizen of the Reich'' (Reich here refers to the Kaiserreich, not the 3rd Reich). They believe that Germany never surrendered in WW1 and should go back to its borders of 1914. The federal republic, the courts, and police etc are all illegal institutions that have no right to rule in Germany.
Now they are a pretty diverse group. From people that declare themselves Kaiser, conspiracy nuts, some kind of ''Forrest wizards'' and hardcore Neo-Nazi they basically have everything.
They have been operating for decades now but the last decade or so have somehow attracted way more Neo-Nazis and have gotten violent. Some guy shot a cop a few years ago which is a big no-no in Germany and the cops are going to come down on you hard. So the government declared everyone involved with that movement unfit to have a gun license.
They had 1200 registered gun owners in March but by July 300 of them have been successfully disarmed. One of them even had a Panzerhaubitze and a tank
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https://www.dw.com/en/german-authorities-raid-suspected-far-right-reichsbürger-terror-cell-members/a-43299600