From what I know, during WW1 my great-grandfather, who was from the Croatian town of Rijeka, was conscripted to the Austro-Hungarian army. There he fought on the eastern front, where he was at one point captured by the Russians. Could he have been taken as a prisoner during the Battle of Galicia?
From his time as a prisoner in Russia my family had a communist party membership card (which has been lost) and this document. As it seems this document was issued in a hospital in Tsaritsyn (now Volgograd). Was that a hospital for prisoners of war?
From what I can tell, in the upper left corner, it says (in cyrillic script) that the document was issued by the RSFSR. What did the RSFSR do with Russian war prisoners. Also a few rows under, it says (at least I think) okhrana (the old Russian secret police), but the year in which the document is placed is 1918. How could that be possible i okhrana was dissolved in 1917 ?
If the document is dated in the October of 1918 and at that time the city was being besieged by the White Army, what was my great-grandfather doing there at the time?
Also if some of you know russian, could you please further clarify the document to me since I haven't been able to translate and interpret the document myself.
The imgur document link : https://imgur.com/a/Iwo8Q7w
The stamp, as best as I can translate it, says:
RSFSR
Soviet/council of workers' and peasants'
deputates
administrative division
security/defense/guard/intelligence sub-division (охрана in Russian can also just mean "security, guard, escort")
The document says that the bearer is indeed the Serbian national "Zorielov Georgievich XXXX", living in Tsaritsyn, as can be seen from the certificate/attestation of illness issued by the office of records.
I hope this helps in any way, unfortunately, I can't say more concerning the historic background.
So, I'm not a historian, but I did found some interesting information. I'll try to keep it short (since it takes too much time to translate it all, huh), sorry for possible clumsiness.
Russian Empire was one of the largest counties of the War by the count of captured soldiers, most of whose were Austrian-Hungarians. Russian General Staff ordered to sort prisoners by ethnic identity: slavs had to be housed in European part of Russia, so they didn't have to suffer a long transportation, unlike Germans and Hungarians who were mostly sent in Siberia. At the end of 1914 it was decided to create a yugoslavia volunteer corps, which consisted of deserters and Austrian-Hungarian POW. It was done by the midyear of 1916 and the First Serbian Corps was quartered near Odessa, with the Second on it's way.
A newly-converted soldiers lost their POW status, took the oath to Serbia and were put under command by invited serbian officers. Soon they made their combat debut at the Battle of Dobrich, which was lost by Russian army. Serbians proved their courage and heroism, but suffered big casualties - this took a great toll on Serbian morale. The situation was worsen by ethnic conflicts between serbs and croats, so those corps suffered moral decay. Soldier count drasticaly dropped after February revolution: only 20000 remained (out of 40000). After October revolution some soldiers were moved to Murmansk and Siberia, where they fought on "white" side, while other joined Bolsheviks.
Now, to the most interesting part. I found a very glaring example of serbian/croatian who served in Austria-Hungarian, Russian Empire and Bolshevik's army - Oleko Dundich. Citing Great Soviet Encyclopedia:
...In 1914 he was recruited as a private in the Austro-Hungarian Army. During the First World War of 1914-1918 in May, 1916 Dundić was taken prisoner by Russian troops near Lutsk. He volunteered to join the First Division of Serbian Volunteer Corps in Russia. From the middle of 1917, he was a member of the Red Guard (presumably in Odessa). In March, 1918, he headed a guerrilla squad in the region of Bakhmut that later joined the Morozov-Donetsk division, which retreated together with the army of K.E. Voroshilov towards Tsaritsyn in June 1918. He participated in the defence of Tsaritsyn as a member of an international battalion, then with cavalry brigades of Kryuchkovsky and Bulatkin. From 1919, he served in the Special Don Caucasus Division of Semyon Budyonny (later in the cavalry corps and the First Mounted Army). He was deputy regiment commander, special aide to Semyon Budyonny, commander of mounted division at the headquarters of the First Mounted Army. Dundić took part in numerous battles and he was wounded several times. The legendary courage of Dundić brought him ardent love and popularity among Budyonny's troops. From June 1919 he was the deputy commander of the 36th regiment of the 6th cavalry division. He was killed in battle near Rovno, Ukraine, and awarded the Order of the Red Banner
So, to your great-grandfather. It's still speculation, but now based on newly acquired information. He deflected or was captured, perhaps indeed in Battle of Galicia, or later, like Dundich did. I think he was a part of Serbian Corps as well, because all of them took the oath to Serbian king, which would expain this strange note in your document about "Serbian national". I thought about mentioned "office of records", I think it was a military commissariat where he was put on record, now by new authorities. Since he had communist party membership card and was seemingly put on record by army, I thing it's safe to say that he could've participate in battle of Tsaritsyn as a member of an international battalion, just like said Oleko Dundich. There's probably a lot more to be researched, but here's all connections I could've made without facing too deep in specialist literature.