What's the evidence for such claims? Accusations or rape is just ridiculous delirium that the West throws at any army they did not like
The claims are being made by refugees and people in Syria willing to speak up about it.
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starting from the Goebbels accusations against the Red Army. There is no basis to believe that any army ever commited any large-scale rape against even foreign people not to say own people.
I suppose it's just a coincidence that German hospital records show that abortion rates began to surge in parts of Germany within months of being occupied by the Red Army. The thousands of personal accounts from women claiming to have been raped are lies, just as are the accounts of men who served in the Red Army claiming to have witnessed it. I am not sure why so many are so skeptical against this idea--nobody is judging Russia today for these actions, nor does it doesn't diminish the accomplishments of the Soviet Union in its victory in the Great Patriotic War. Many rapes of German women likely occurred by American soldiers as well as Soviet. I take objection to your statement that there is no basis to believe that any army ever committed large-scale rape, since, historically, that was actually a norm for many cultures post victory, and they freely admitted it and wrote about it.

It is quite evident that Syria is putting down an armed rebellion supplied from abroad.
This does not justify the massacre of innocent men, women, and children.