Steve, I think what I have been describing is the current process, rather than one that has happened in the past, so there are not really much in the way of completed examples to identify.
Various countries, several of which I have experience, have been moving steadily to the left over the last 40-50 years or so, the 'social democratic' parties in the UK, Europe, Australia/New Zealand along with their left wing 'establishments' have pushed mainstream politics a long way to the left but have done so quite slowly.
This came to a head in 2016, 'populist' pushback in the shape of Trump and Brexit, the emerging agenda of intersectionalism, looked threatened for a moment, but it has been ramped up and up such that it is now virtually the only agenda in education and the public sector. It is used to counter and destroy any figure in these institutions who do not support the Hard Left/Common Purpose viewpoint.
The 'hardcore left' reaction that I talk about has really only really emerged as a practical force in the last 6-7 years but it has come a long way, particularly in the US. It is, I believe driven and financed by globalist money from tech and media giants, organisations such as 'Open Society' and anti western interests in countries like Saudi, Qatar and China.
Although this process is occurring in the uk, it is most obvious in the US. I think it is self evident.