https://en.wikipedia.org/wiki/International_Brigades
This always makes me think how much the world has changed. Can you imagine travelling today to a foreign country ready to die for fighting oppression? I have never seen such kind of conviction in my life.
Not quite as many as in the stalinist-run International Brigades, but certainly over 10 000 volunteers. And not just from the fascist-run Germany or Italy, but a large number of countries. General Franco even turned down legions from Greece and exiled White Russians.
The British Communist party had found George Orwell "politically unreliable", and as we later saw, for a good reason. Likewise, Franco must have considered e.g. the Russian volunteers "politically unreliable", and probably that was also for a good reason - it would be surprising if such volunteer forces were not infiltrated by the NKVD and whoever.
That's exactly what young people from all over the world think what they do when they travel to Syria and join ISIS.
From their point of view, they are fighting against a dictator(true) in order to create a regime most of the people there want(a theocracy).
While doing so they oppress other people, like the communist did in the Spanish civil war.
Maybe we are more realistic now. I would have tried to run as far away as possible from that war (or any other). My grandpas weren't so lucky.
About what happened, I try to listen, learn and then mostly shut my mouth. I'll only say that real life isn't a clear cut story of good and evil people. Look at Syria now and you would find a more accurate image than that of "fight against fascism".
There were russians who fight in Ukraine and if you ask ISIS fighters they will tell you they are fighting to spread the-one-true-religion which is similar to fighting to spread the-one-true-ideology with minor differences.
Also fighting oppression was what was sold to US soldiers going to the Mid East at least partially.
The official line from Putin is that all Russian soldiers fighting alongside the independentists are volunteers, but that sounds as true as his earlier lie about the "green men" being local militias.
Now there is a formal army of "unrecognized republics" formed from same volunteers plus a lot of locals who are just in it for the pay. The morale is correspondingly much lower.
AFAIK Russian army did some heavy lifting but not on the regular basis. They merely protect "republics" from collapse.