In 1529, Suleiman the Magnificent led an Ottoman-Transylvanian force to attack the city of Vienna. They besieged the city for more than two weeks, but failed to capture it and were forced to withdraw.

Let us suppose they captured the city. What would change?
 
Nothing too harmful for the Habsburgs in the short run as they retreat to Linz. Zapolya consolidates Hungary and has a garrison in Vienna to defend Hungary.

The Ottomans have forces ready to invade elsewhere rather than fighting endless battles in Hungary for 200 years. An invasion of Southern Italy is a sincere possibility or major campaigns in Persia.

Vienna may likely be reconquered by the Habsburgs. Ferdinand has only Bohemia from his inheritance. But by that time Zapolya has Hungary secured.
 
In 1529, Suleiman the Magnificent led an Ottoman-Transylvanian force to attack the city of Vienna. They besieged the city for more than two weeks, but failed to capture it and were forced to withdraw.

Let us suppose they captured the city. What would change?


The timing was all wrong: the siege began few months after France signed peace with Charles leaving him with plenty of resources to subdue whatever was left out of the League of Cognac. It could be different if Suleiman started offensive in 1526 - 27 and did not stuck with something of a mostly token importance, like Vienna, but just established a blockade with a small part of his force and proceeded with destroying the countryside as far and wide as he could, preferably beyond Hapsburg hereditary lands: this could force Charles to direct Frundsberg and his landsknechts to Austria instead of Italy thus seriously improving strategic situation for the League of Cognac.

Of course, standard Ottoman logistics was putting serious limitations on their ability to conduct the deep operations but they had the Crimean Tatars (not sure if they participated in OTL campaign but they already were the Ottoman vassals), irregulars, Moldavian and Serbian troops and 6,000 of Transylvanian cavalry under John Zapolya. These troops had been faster and less dependent on the organized supply system than the Janissary and could do enough of a damage to attract attention of Charles.
 
The timing was all wrong: the siege began few months after France signed peace with Charles leaving him with plenty of resources to subdue whatever was left out of the League of Cognac. It could be different if Suleiman started offensive in 1526 - 27 and did not stuck with something of a mostly token importance, like Vienna, but just established a blockade with a small part of his force and proceeded with destroying the countryside as far and wide as he could, preferably beyond Hapsburg hereditary lands: this could force Charles to direct Frundsberg and his landsknechts to Austria instead of Italy thus seriously improving strategic situation for the League of Cognac.

Of course, standard Ottoman logistics was putting serious limitations on their ability to conduct the deep operations but they had the Crimean Tatars (not sure if they participated in OTL campaign but they already were the Ottoman vassals), irregulars, Moldavian and Serbian troops and 6,000 of Transylvanian cavalry under John Zapolya. These troops had been faster and less dependent on the organized supply system than the Janissary and could do enough of a damage to attract attention of Charles.

Suppose Suleiman invaded earlier or the Italian War of the League of Cognac lasted a bit longer (well into 1531 or 1532), thus dividing the attention of the Habsburg. What would happen then ? Would the Ottomans make the archduchy of Austria some sort of vassal and annex all of Hungary directly into the empire ?
 
Suppose Suleiman invaded earlier or the Italian War of the League of Cognac lasted a bit longer (well into 1531 or 1532), thus dividing the attention of the Habsburg. What would happen then ? Would the Ottomans make the archduchy of Austria some sort of vassal and annex all of Hungary directly into the empire ?
Pretty unlikely who Vienna and Austria will be allowed to remain in possession of the Ottomans...
 
Suppose Suleiman invaded earlier or the Italian War of the League of Cognac lasted a bit longer (well into 1531 or 1532), thus dividing the attention of the Habsburg. What would happen then ? Would the Ottomans make the archduchy of Austria some sort of vassal and annex all of Hungary directly into the empire ?

If the plans related to the second siege are indicative of the earlier attitudes, Suleiman potentially could create a vassal state out of a part of Austria but doing or not doing that would be of a marginal importance comparing to a potential shift of a balance between Charles and League of Cognac, for example, Habsburg loss of Italy with the numerous butterflies and an absense of the Sack of Rome (which may change Henry’s activities in England).

Of course “marginal importance” is used strictly within a broader European context. Expansion of the Ottoman influence to Austria or even putting Austria within a reach of a routine raiding would mean a lot for the local population.
 
Making Austria a vassal seems unlikely to me. It belongs to Charles V who will never accept such conditions as his prestige is under threat. Giving Vienna and other border areas to Hungary is however possible. The Tatars, Hungarians, Akinci's might likely use the region as a base to raid along the Danube and Bohemia & Moravia
 
Making Austria a vassal seems unlikely to me. It belongs to Charles V who will never accept such conditions as his prestige is under threat. Giving Vienna and other border areas to Hungary is however possible. The Tatars, Hungarians, Akinci's might likely use the region as a base to raid along the Danube and Bohemia & Moravia
I said “part of Austria”, which was more or less plan of the XVII campaign. Of course, Charles would have to do something about this, which is the whole point: with a proper timing, he would be looking for two wars simultaneously and I’m not sure if he had enough resources.
 
Hmm, with an extended Italian War of Cognac lasting well into the early 1530s, would the Habsburgs even have enough resources with them to fight both France, the Papacy, and their allies along with the Ottoman Empire ? The Habsburgs have way too many enemies and fronts to defend.

This is not even mentioning the growing Protestant movement that the Habsburgs need to stamp out within the German principalities . . .

With the Protestants, the French, the Papacy and their allies, and now the Ottomans in Vienna . . .
 
Hmm, with an extended Italian War of Cognac lasting well into the early 1530s, would the Habsburgs even have enough resources with them to fight both France, the Papacy, and their allies along with the Ottoman Empire ? The Habsburgs have way too many enemies and fronts to defend.

This is not even mentioning the growing Protestant movement that the Habsburgs need to stamp out within the German principalities . . .

With the Protestants, the French, the Papacy and their allies, and now the Ottomans in Vienna . . .

That’s the general idea but the Protestants are tricky issue: there were plenty of them among Frundsberg’s landsknechts but they were loyal at least as long as there was a chance to get paid or to get loot: their rebellion which ended with a Sack of Rome targeted Charles’s enemies.
 
That’s the general idea but the Protestants are tricky issue: there were plenty of them among Frundsberg’s landsknechts but they were loyal at least as long as there was a chance to get paid or to get loot: their rebellion which ended with a Sack of Rome targeted Charles’s enemies.

So do you think that the at least part of the archduchy of austria (minus say Tirol and the northwestern bits) would be vassalised with the Habsburgs divided into multiple wars and fronts ?

The Habsburg could also move to Prague as the centre of the central european empire.
 
I said “part of Austria”, which was more or less plan of the XVII campaign. Of course, Charles would have to do something about this, which is the whole point: with a proper timing, he would be looking for two wars simultaneously and I’m not sure if he had enough resources.

Fair enough. It might be added to Zapolya's realm. There is no need for Hungary to be stronger. But a few parts of todays Austria won't make them. As long as Ferdinand is kept away from Hungary. If Hungary still turns Calvinist then it is a win win situation as it will be harder to get a land hostile to a zealous Catholic dynasty.
 
So do you think that the at least part of the archduchy of austria (minus say Tirol and the northwestern bits) would be vassalised with the Habsburgs divided into multiple wars and fronts ?

The Habsburg could also move to Prague as the centre of the central european empire.

OK, let me explain an idea more systematically:

1. Soleiman’s offensive is synchronized with the actions of the League of Cognac (which was reasonably successful until Charles mobilized his resources).
2. Instead of concentrating on taking Vienna, Soleiman is just blocking it with a small part of his force and concentrates on doing as much damage as possible to the Austrian lands with the raiding parties going beyond these lands creating enough concern in the HRE. As a side show, some of the light troops can harras the Hapsburg-held Hungary but this is not critically important for the general strategy. The main body of the Ottoman army can advance slowly to provide “support base” for the raiders but without getting bogged down into the sieges (there should be plenty of places without the adequate defenses).
3. The Ottoman (Tatar, Serb, Moldavian, etc.) raiders are causing enough concern within the HRE to force Charles to send Frundsberg & Co against the Ottomans instead of Italy.
4. League of Cognac maintains a numeric advantage in Italy and elsewhere and can grab some disputed or Hapsburg-held territories (Milan would be one of the primary targets).
5. Charles does not have money to pay his troops (as in OTL) and the landsknechts sent against the Ottomans can’t expect too much of a loot. In Italy Spanish troops are not numerous enough to defeat the opponents and also are not being paid. With armies of the League being bigger in numbers and the French still participating, retaining Naples is probably the best case scenario for the Spaniards.
6. Without payment and hope for plunder the landsknechts would rebel sooner or later and Frundsberg’s authority is not absolute. Perhaps the HRE Diet can vote for some subsidies and this may stretch fighting for a season or two but not forever. The problem is that at that time the Western warfare was not up to the task of reconquering Hungary even if some field victories can be scored.
7. From the Ottoman perspective, there is plenty of loot and a chance of moving the “operational base” somewhat to the West making Austria and HRE vulnerable. If they manage to solidify the gain of some territory (say, Eastern part of Austria), they may make it into a vassal “kingdom”, which would cost them nothing even if it is going to be lost sooner or later. The important thing is to “open” the HRE to the future raids.

Of course, the above schema requires certain shift in the Ottoman military mentality but as was demonstrated in OTL later, they were quite capable of using the raiding abilities of their vassals, especially Tatars. OTOH, they still had something of an obsession with the sieges. Of course, the big cities were a potential source of a greater loot but countryside was a good source of the slaves and other goodies and garrisons of the fortified places were usually not big enough to “project power” too far beyond the city walls.
 
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