[PGR88]

Here is a good place to start

https://en.wikipedia.org/wiki/Russo-Turkish_War_(1877–1878)

Russia had great dreams of empire, but also had very legitimate historical grievances against the Ottoman Caliphate, their Islamic hatred of Christianity and continual oppression of the slavs.

[MacNaughton]

Thanks for the link. Now I see. The UK was still playing the “Great Game” against Russia.