I'm not a historian, but I do some reading on history. I was in a book about the history of Florence when the Treaty of Vienna was mentioned briefly, and as someone not particularly well-versed in 18th-century politics, the whole thing struck me as a little absurd and farcical. The end result was a lot of different nobles shuffling their possessions around. The Duke of Saxony became King of Poland. The King of Poland became the Duke of Lorraine. The Duke of Lorraine became the Duke of Tuscany (and Tuscany wasn't even in the war, to the best of my knowledge!). The Duke of Parma became the King of Naples and Sicily. Parma was, finally, given over to Austria.
How was this particular series of trades worked out between the various belligerent parties? Who negotiated these trades? Why did they decide to trade thrones instead of directly ceding territory or other concessions?
More importantly, how did the various territories involved react to suddenly having a strange foreign ruler placed in charge of them? I have an idea of how it went over in Florence (i.e. not well), but any details on the other territories involved would be quite welcome.
Thanks in advance for your time!
I'm going to answer this question by first writing about the concept of ceding and trading territory in the 18th century, and then i'm going to address the titles and people individually. Since there were good reasons for these territories to change hands, and the territory swaps weren't arbitrary.
The main reason these titles were ceded instead of territory changing hands was in order to maintain a balance of power in Europe. Therefore if for example Spain annexed Naples, Spain might become too strong, but if a relative of the Spanish King gained the throne of Naples that was more acceptable, since even though he would obviously be an ally of Spain, in a few generations this alliance might end, and Naples would still retain some independence. Finally to a certain extent Kings had different titles to rule over different territories, and ceding titles was one way to cede territory.
The Treaty of Vienna ended the war of the Polish Succession, there were two claimants to the throne, Stanislaw Leszcynski and Augustus III. Augustus III was also the Elector(Duke) of Saxony. Poland at the time had an elective monarchy, which meant that after the death of the previous king the nobles would gather and vote for a new king.
Augustus II who was the father of Augustus III had originally been elected King in 1697, however after Sweden invaded Poland they installed Stanislaw as the King of Poland. Augustus II eventually managed to reclaim his throne in 1709 and drive out Stanislaw.
Stanislaw was father-in-law of Louis XV of France, and therefore after Augustus II died, he returned to Poland in 1733 with French support and was elected as King. A different and smaller group of Polish nobles elected Augustus III, who was the son of Augustus II as King.
Poland reacted well enough to being ruled by Augustus III since he arguably had a much better claim than Stanislaw. Augustus also didn't put a lot of effort into governing Poland, this kept unrest at low levels since the nobles had a lot of autonomy and therefore little reason to rebel. However the weak rule of Augustus III weakened Poland, and eventually led to the partitions of Poland.
Stanislaw become the Duke of Lorraine since Lorraine bordered France, and he was the father in law of Louis XV of France, therefore when Stanislaw died Lorraine was inherited by Louis XV and became a part of France. There were minor insurrections against French rule in northern Lorraine which was more Germanic than southern Lorraine which was more French.
The former Duke of Lorraine was Francis III Duke of Lorraine (Francis I Holy Roman Emperor). He was married to Maria Theresa who was the heir to Austria, and whose succession would eventually spark the war of the Austrian succession. There were a lot of succession wars during the 18th century. Francis wasn't given the Duchy of Tuscany, he was only widely recognised as the heir to the Duchy of Tuscany.
Since the previous duke Gian Gastone didn't have any sons. The question of who would succeed Gian had been going on for many years even before the war of the Polish succession. In fact the previous treaty of Vienna in 1731 was about who would inherit Tuscany.
The 1731 treaty of Vienna said the heir to Tuscany would be Charles I Duke of Parma(Charles III King of Spain). Tuscany was a small country and therefore had to abide with the decisions the great powers made. Tuscany was in Northern Italy and was close to Austrian possessions, by the end of the war of the Polish Succession. Austria controlled northern Italy, while Spain controlled Southern Italy.
After the death of Gian in 1737 Francis became Duke of Tuscany, the treaty of Vienna 1738 merely recognised this fact. It wasn't until after Francis's son Leopold inherited the duchy that there was some serious unrest. Leopold was an unpopular ruler among the nobles because he was too reformist. For example Leopold abolished the death penalty in 1786, this and other reforms made him unpopular.
Austria annexed Parma because they had occupied it during the war. Austria ceded the Duchy of Parma back to a Spanish prince after the end of the war of the Austrian Succession in 1748. Parma didn't offer any resistance to being recaptured by Spain.
Naples and Sicily were in a personal union under Spain since the 15th century. After the end of the war of the Spanish succession in 1714, Naples and Sicily were placed in a personal union under Austria. Charles III who was a Spanish Prince became the Kings of Naples and Sicily, in exchange for giving up Parma and his claim to Tuscany.
Charles was very popular in Naples and was blessed by Cardinal Pignatelli, the archbishop of Naples when he arrived there. Charles was popular partly because he was the first King of Naples to live there since the 15th century. Charles inherited the Spanish throne in 1759, and Naples and Sicily were ruled by his son Ferdinand I(of the two Sicilies).
In summary all of these titles changing hands resulted in a lot of the territory going back to their rightful rulers. Apart from Lorraine and Parma, the new rulers of the territories ended up being as popular, if not more popular than the previous rulers.