WI Maximilian III had defeated the supporters of Sigismund III Vasa in the Battle of Byczyna ? Could we have a Habsburg Poland, or would he have been defeated later by the Polish nobles? And, if he becomes king, what would do Sigismund?
Sigismund's attempt to claim the Swedish throne fails, however, that is not the end of his career claiming thrones. He lives in Austria for several years, until tensions between Poland and Muscovy turn into war. Sigismund has a claim to the Muscovite throne, and as Maximilian gains the upper hand, decides to place Sigismund upon the Muscovy throne, in order to have a friendly monarch to his east.
So he is inpopular and Poles didn't not want to fight for him even when he was King of Poland. Why should they fight for him later? In XVIIth century Polish-Lithuanian Commonwealth wasn't particularly aggressive country. The intervention during Times of Troubles was Sigismund's idea, because he was obssessed with idea of making Russia Catholic. The noblemen weren't very happy about it - they prefered peace, when they didn't have to pay higher taxes or go for war.His resources from Sweden cut-off, and facing dissension among Polish nobility because of his military demands to meet the challenges of Maximilian military challenge, Sigismund suffers a massive defeat at the hands of Maximilian's army.
What claims to Muscovite throne? Sigismund's son Władysław (later king Władysław IV) was invited by Russian boyars to become tsar in 1610, after Poland-Lithuania defeated Muscovite army and captured Tsar Vasiliy Shuisky; however, only if Władysław would convert to Orthodoxy. Since Sigismund was fanatic Catholic, it didn't work because he wanted the throne for himself to make Russia Catholic. Of course Orthodox boyars refused, and Polish intervention in "Tomes of Troubles" ended in failure. And the "Times of Troubles" started with the end of Rurik dynasty. The only claim to Muscovite throene Sigismund had was the fact that he won the war and captured the tsar. Since it didn't happen ITTL, no claims.
Anyway, Muscovites would have never accepted a Catholic ruler, and I doubt if Maximiliam would manage to convince Polish and Lithuanian noblemen to fight long, bloody war to put Sigismund on Muscovite throne.Your quite right. I was looking at the truce which granted the Commonwealth Smolensk, and in that it mentioned that Sigismund had given up his claim on Muscovy, but I didn't look any further, so I didn't realize the claim was based on conquest, not blood. My bad.
So he is inpopular and Poles didn't not want to fight for him even when he was King of Poland. Why should they fight for him later? In XVIIth century Polish-Lithuanian Commonwealth wasn't particularly aggressive country. The intervention during Times of Troubles was Sigismund's idea, because he was obssessed with idea of making Russia Catholic. The noblemen weren't very happy about it - they prefered peace, when they didn't have to pay higher taxes or go for war.
And it is this lack of desire to pay taxes that Maximilian is going to have to work on during his reign. In Hungary and Bohemia the nobility were rather quickly overmatched by the Hapsburgs, and forced to accept permanent Hapsburg rule. Maximilian I of Poland would die before his brother, the HRE Matthais, so Ferdinand (Future HRE Ferdinand II) would have about a year to get himself elected King of Poland. Maximilian was Ferdinand's regent OTL, so the same thing could happen. This would drag Poland directly into the 30 Years' War as a Hapsburg family possession.
And it is this lack of desire to pay taxes that Maximilian is going to have to work on during his reign. In Hungary and Bohemia the nobility were rather quickly overmatched by the Hapsburgs, and forced to accept permanent Hapsburg rule. Maximilian I of Poland would die before his brother, the HRE Matthais, so Ferdinand (Future HRE Ferdinand II) would have about a year to get himself elected King of Poland. Maximilian was Ferdinand's regent OTL, so the same thing could happen. This would drag Poland directly into the 30 Years' War as a Hapsburg family possession.
No Polish king ever managed to convince Polish noblemen to pay higher taxes, unless they faced a direct danger to their country.
I doubt Maximilian would have done it. In Hungary and Bohemia Habsburgs were hereditary rulers,
while in Poland-Lithuania kings were elected, and their position was also weakened by the Sejm (Parliament), constitution Nihil novi (no new law without approval of the Sejm) and privilege of Koszyce (no higher taxes without noblemen approval).
What is more important, at the end of XVI century Polish-Lithuanian Commonwealth felt actually quite safe from any foreign threat. Sure, Moscow, Turkey and Tatars might have hurt it, but nobody seiously believed they might conquer it. Hungary and Bohemia were smaller and they had all power of Turkey right at their doors. You don't question your ruler when there is really powerful enemy right across the border.
And dragging Poland-Lithuania into 30 Years war wouldn't have been easy either. Even if we assume the Counterreformation is as strong as under the rule of Sigismund III IOTL, the Commonwealth still would have been quite tolerant and not particularly eager to fight in a religious war. Maximilian, as king of Poland, would have had to swear to honor the Confederacy of Warsaw (law from 1573 forbidding any religious persecutions in the Commonwealth).
Also, Polish-Lithuanian noblemen most certainly wouldn't have thought about themselves as Habsburg family possession. In their eyes Maximilian would have been an elected king, with no right to decide who would be his successor, and if he had made them pay higher taxes, Ferdinand's chances for Polish throne would have been nonexistent.
To achieve all what you propose Maximilian would have had to break Polish-Lithuanian noblemen and power of Sejm. It was possible only by civil war, because noblemen most certainly would have fought for their privileges, for their Aurea Libertas (Golden Freedom). Since Poland-Lithuania was quite a big country forces to achieve that would have had be enormous - I doubt Habsburgs could win such a war.
BTW, I checked some facts, and discovered that Byczyna (place of Maximilian defeat) was in Silesia, in that time part of HRE. During election of the king of PLC, there were riots caused by Maximilian followers. Since they tried to use force during election, they were discredited together with their candidate (later using force during election wasn't seen as such crime). Sejm declared Maximilian's followers traitors. Maximilian tried to fight, but he lost race to Cracow. The town was occupied by Sigismund's follower, Polish chancellor Jan Zamoyski (very influential politician in Poland-Lithuania). Maximilian's attempt to capture it (with help of some local Germans) ended with defeat and he had to withdraw to Silesia. Zamoyski went after him across the border (he had Sejm's approval for extraordinary measures) to finish the threat once and for all. In other words, Maximilian lost his chances for Polish crown even before battle of Byczyna. Even assuming Zamoyski was defeated (quite possible), Maximilian's position was very weak. His Polish followers were in disarray and considered traitors, most of Polish-Lithuanian noblemen supported Sigismund (or rather became ferociously anti-Habsburg). HRE's intervention would have been considered a foreign invasion and imperial forces would have met with very strong resistance, extremely hard to break.
This period of peace actually works against the Polish-Lithuanian nobility. If Maximilian is the King of Poland, then there is really no one who can intervene against him. Sweden is occupied by Sigismund's continued attempts to retake the throne, the Rudolf II, leader of the Austrian Hapsburgs, is actively in support of his brother Maximilian in his quest for greater power in Poland, and Russia is in the midst of a messy civil war. If Maximilian forces a civil war, then it will be him and the Hapsburgs against the Polish nobility, with no foreign power to step in and help the Poles. This period last about 20 years, from the early 1590's to 1618, when the 30 Years' War begins. That is enough time to erect the structures of Hapsburg hereditary power in Poland, and get through the first major nobles revolt against the expanded Royal power.
Again, previledges only exist as long as they can be defended. If a strong king has enough support in a civil war against his nobility, he would be able to break them. That it didn't happen in Poland didn't mean that it couldn't, it just means that no ruler was able to role the right dice. And no Hapsburg ever had the chance to role in this particular position.
Mu POD is that Rudolf supports Maximilian's bid to become King of Poland. This bid was based on the idea that Sigismund was illegally elected, and therefore Maximilian was the rightful king. Whether or not Max and his followers were outlawed by Sigismund's faction, it is force that determined who the outlaws would be. If Maximilian had won that battle, and with his brother's support continued the war, and then won the war, then the Polish nobles who had been anti-Hapsburg would make their peace and that would be that. As it was OTL he didnt succeed on the battlefield, and this meant that the Sejm's decision stood. Change who wins, and you change what is and is not legal, and who is or is not an outlaw.
Actually, Sigismund was elected very legally. His election was accepted by interrex (acting ruler between elections), the Primate od Poland Stanisław Karnkowski. It was Maximilian who was proclaimed king of Poland in Olmutz (today Czech Republic), well outside Polish border. And, as I mentioned later, battle of Byczyna was actually not the beginning of Max's fight for Polish crown, but coup de grace by Zamoyski in Sigismund's name. Maximilian already lost most of noblemen support and he could get back only leading HRE's army. And that would mean full scale war.
OTOH I must admit, that your idea of Maximilian getting support from cities and towns is very good. IOTL he simply didn't make it in time to Cracow. If he occupied Cracow before Zamoyski, then, well... his Polish followers might have gathered under his banner and Max's chances would have been bigger. But remember, his Polish followers (Zborowski family) were also noblemen obssessed with their privileges. They opposed Sigismund, cause he was supported by Zamoyski, their personal enemy. If Habsburg decided to break Polish noblemen he might have lost a lot of his followers.
Anyway, theoretically, with full HRE's support Habsuburg might have got Polish crown. To keep it, however, would have been much harder. Also, I doubt if HRE really wanted such a war.
But, and WI Maximilian is a little more succesful during the first actions. Let's say he is able to occupy Cracow, and he wins the next battle as well (only a small victory, not a decisive one). Also, imagine that Sigismund goes to Poland to defend his crown, and by chance during a battle he is hurt and dies some days after. Then you have the elected king dead, and Maximilian controlling Cracow. What could happen?