I admit my ignorance about such things but could someone please explain how it is that an individual, in this case Yevgeny Prigozhin is able to possess or control a private army?

I feel naive in regard to my understanding of this but it seems to me that no democracy would tolerate such a situation and equally or perhaps even more-so, no autocracy or dictatorship would do so, either.

Is this simply allowed because of Prigozhin's relationship with Putin or am I missing something? I wonder, too, do other such private armies exist in the World?

Yes, I'm aware that criminal gangs and organisations exist and may be very powerful but, at least to me, they don't seem to be 'armies'.

I'm also, of course, aware that there have been and probably still are many guerilla groups headed by a charismatic individual who leads a significant group of a society in rebellion against its government and which may wage 'warfare' in a military style but, again, that seems different to the Prigozhin situation.

I apologise that this comment is not exactly on topic but to me it does seem related and relevant and I suspect that I may not be the only person who is astonished that an organisation such as the Wagner Group is countenanced.