Sviatoslav I was a very active leader of the Kievan Rus' who led several military campaigns in multiple directions, destroying the Khazar Khaganate and briefly conquering Bulgaria. The latter conquest led to a war with the Byzantine Empire, which finally put an end to his string of victories by defeating the Rus' in the Battle of Arcadiopolis and the Siege of Dorostolon.

In the first battle (Arcadiopolis) the general in charge of the Byzantine army, Bardas Skleros, dodged a bullet when a Pecheneg soldier delivered a sword blow to his head, which was protected by a helmet and thus suffered no harm. What if the Pecheneg struck the general somewhere else and killed him, throwing the outnumbered Byzantines into chaos and preventing them from scoring a critical victory?

Could Sviatoslav establish a "Russo-Bulgarian Empire" of sorts? He transfered his capital from Kiev to Pereyaslavets, located in the Danube Delta, probably to stay closer to the front line in the south and have a tighter control over the trade along the river.

Here's a map of his conquests and sphere of influence (orange) in 971. Could they be consolidated into a single empire if he doesn't die prematurely?

1024px-Sviatoslav1.png
 
Sviatoslav I was a very active leader of the Kievan Rus' who led several military campaigns in multiple directions, destroying the Khazar Khaganate and briefly conquering Bulgaria. The latter conquest led to a war with the Byzantine Empire, which finally put an end to his string of victories by defeating the Rus' in the Battle of Arcadiopolis and the Siege of Dorostolon.

In the first battle (Arcadiopolis) the general in charge of the Byzantine army, Bardas Skleros, dodged a bullet when a Pecheneg soldier delivered a sword blow to his head, which was protected by a helmet and thus suffered no harm. What if the Pecheneg struck the general somewhere else and killed him, throwing the outnumbered Byzantines into chaos and preventing them from scoring a critical victory?

Could Sviatoslav establish a "Russo-Bulgarian Empire" of sorts? He transfered his capital from Kiev to Pereyaslavets, located in the Danube Delta, probably to stay closer to the front line in the south and have a tighter control over the trade along the river.

Here's a map of his conquests and sphere of influence (orange) in 971. Could they be consolidated into a single empire if he doesn't die prematurely?

1024px-Sviatoslav1.png
IMO, this is unlikely. His "mobilization" capacities had been quite limited: it seems that most of the time he was operating with just his personal military band. Then, the whole situation back home was quite fishy and produced more than one theory: after defeat in Bulgaria he spent the whole winter on the lower Dnieper and when finally decided to get back to Kiev, did it with a very small band (was it all that was left or were there other considerations?) so it was successfully ambushed by the Pechenegs. Presumably, his main "voyevoda" proposed to ride to Kiev but by the reason unknown he decided to go by the boats disregarding the river rapids and (known) hostile Pechenegs.

One of the theories is that he was no actually welcomed in Kiev where the Christian party got an upper hand. According to the same theory this was the reason for his attempt to create a new state in Bulgaria. This does not explain the small numbers but, him being all his career pretty much just a successful military leader, we can at least assume a possibility that, with his luck finally running out, so did the loyalty of his troops and especially of the Pecheneg contingents.

Then, as far as his military abilities are involved, he was successful against already dying Khazar Kahanate and against the neighbors but description of his battle against the Byzantines (at least as presented by Lev Deacon) is not very impressive. It looks like the Russian troops fought on foot forming something like Scandinavian shield-wall without any ability to maneuver. Byzantine warfare was much more sophisticated and they had more resources so probably sooner rather than later they'd kick him out of Bulgaria. There is no reason to assume that Svyatoslav possessed any noticeable administrative or diplomatic skills (Kievprincipality was administered by his mother and after her death he put his young son on the throne). "You can conquer empire sitting in a saddle but you can't rule it from the saddle".
 
IMO, this is unlikely. His "mobilization" capacities had been quite limited: it seems that most of the time he was operating with just his personal military band. Then, the whole situation back home was quite fishy and produced more than one theory: after defeat in Bulgaria he spent the whole winter on the lower Dnieper and when finally decided to get back to Kiev, did it with a very small band (was it all that was left or were there other considerations?) so it was successfully ambushed by the Pechenegs. Presumably, his main "voyevoda" proposed to ride to Kiev but by the reason unknown he decided to go by the boats disregarding the river rapids and (known) hostile Pechenegs.

One of the theories is that he was no actually welcomed in Kiev where the Christian party got an upper hand. According to the same theory this was the reason for his attempt to create a new state in Bulgaria. This does not explain the small numbers but, him being all his career pretty much just a successful military leader, we can at least assume a possibility that, with his luck finally running out, so did the loyalty of his troops and especially of the Pecheneg contingents.

Then, as far as his military abilities are involved, he was successful against already dying Khazar Kahanate and against the neighbors but description of his battle against the Byzantines (at least as presented by Lev Deacon) is not very impressive. It looks like the Russian troops fought on foot forming something like Scandinavian shield-wall without any ability to maneuver. Byzantine warfare was much more sophisticated and they had more resources so probably sooner rather than later they'd kick him out of Bulgaria. There is no reason to assume that Svyatoslav possessed any noticeable administrative or diplomatic skills (Kievprincipality was administered by his mother and after her death he put his young son on the throne). "You can conquer empire sitting in a saddle but you can't rule it from the saddle".
Yeah, we had a brief conversation on this subject a while back so I figured you'd say that again. Could securing Bulgaria and looting Thrace give Svyatoslav a new lease of life? As for the Byzantines, the Fatimids, who were at the apex of their power back then, were still a threat, especially since they laid siege to Antioch in 970-71.

Speaking of the Fatimids, could one of Svyatoslav's successors convert to Islam to secure an alliance with them? I don't think the alcohol thing would be much of a hurdle, since the Andalusians were known for drinking wine.
 
Yeah, we had a brief conversation on this subject a while back so I figured you'd say that again. Could securing Bulgaria and looting Thrace give Svyatoslav a new lease of life? As for the Byzantines, the Fatimids, who were at the apex of their power back then, were still a threat, especially since they laid siege to Antioch in 970-71.

It did not take a huge Byzantine army to kick Svyatoslav out of Bulgaria. Of course, we can’t completely exclude a possibility you are talking about but he has to be military successful all the time and, IMO, he looks more like a lucky raiding warlord than some kind of a military genius.

To maintain himself in Bulgaria he would need, on a permanent basis, a big loyal military force.In OTL his invading army consisted of his personal military band, allied Pechenegs and, IIRC, even Hungarians. The allied nomads could not be relied upon in a long run and the Russian “reserves” had been quite limited: he and his band were the pagans while Kiev was already dominated by the Christians and it does not look like he got any noticeable support from it during his OTL campaigns. Bulgaria also was Christian so probably not too much support for a pagan ruler (did not happen in OTL).

Speaking of the Fatimids, could one of Svyatoslav's successors convert to Islam to secure an alliance with them? I don't think the alcohol thing would be much of a hurdle, since the Andalusians were known for drinking wine.
Why would any of his successors want alliance with the Fatimids? Christianity was already reasonably strong in the Southern Rus and so was connection to the Byzantine Empire: the trade was still a significant factor and don’t forget that at least initially Svyatoslav invaded Bulgaria on Byzantine’s request. How useful tye Fatimids could be?
 
I would like to add to @alexmilman but from the byzantine perspective even of the rus won killing bardas would not change much if anything emperor Jonh gathers a large force and crushes him in fact the pod the op describes favors the byzantines the death of bardas means that his rebellion would never occur which means that Bardas Phokas nevers gets freed from his exile and so Basil has more time to deal with a weakened bulgaria and can do more not dealing with 2 rebellions.
 
I would like to add to @alexmilman but from the byzantine perspective even of the rus won killing bardas would not change much if anything emperor Jonh gathers a large force and crushes him in fact the pod the op describes favors the byzantines the death of bardas means that his rebellion would never occur which means that Bardas Phokas nevers gets freed from his exile and so Basil has more time to deal with a weakened bulgaria and can do more not dealing with 2 rebellions.
There was, AFAIK, even more from the Byzantine perspective. Svyatoslav spelled out why did he want to set his new capital on the lower Danube: the flows of various goods from various area had been coming through this geographic point. While the Byzantines could tolerate a weak Christian Bulgarian state controlling these flows, having a strong bellicose pagan leader in such a position was a seriously different scenario because he almost definitely would be using this economic factor to his advantage and against the Byzantine interests.
 
So the conclusion is that something catastrophic needs to happen to the Byzzies for Svyatoslav to have a chance in Bulgaria?
 
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