When Emperor Joseph I died on April 17, 1711he left behind two daughters, Archduchesses Maria Josepha and Maria Amalia. Charles, who was at the time still unsuccessfully fighting for the crowns of Spain, succeeded him as King of Hungary, Bohemia, Croatia and Archduke of Austria according to the Mutual Pact of Succession and returned to Vienna.

Joseph I, Holy Roman Emperor
On October 12, 1712 Charles was elected Holy Roman Emperor Charles VI.
In 1708, Archduke Charles had married Princess Elisabeth Christine of Brunswick-Wolfenbüttel the eldest daughter of Ludwig Rudolph, Duke of Brunswick-Wolfenbüttel and his wife Princess Christine Louise of Oettingen-Oettingen.
At age 13 Elisabeth Christine became engaged to the future Charles VI, Holy Roman Emperor, through negotiations between her ambitious grandfather, Anthon Ulrich, Duke of Brunswick-Wolfenbüttel and Charles’ sister-in-law, Empress Wilhelmine Amalia, whose father was Johann Friedrich, Duke of Brunswick-Calenberg and thus belonged to another branch of the House of Guelph.
However, the Lutheran Protestant bride opposed the marriage at first, since it involved her converting to Roman Catholicism, but finally she gave in. She was tutored in Catholicism by her mother-in-law, Empress Eleonore, who introduced her to the religion and made a pilgrimage with her to Mariazell in 1706.

Charles VI, Holy Roman Emperor
Charles VI and his wife Elisabeth Christine of Brunswick-Wolfenbüttel by whom he had his four children: Archduke Leopold Johann (who died in infancy), Archduchess Maria Theresa (the last direct Habsburg sovereign), Archduchess Maria Anna (Governess of the Austrian Netherlands), and Archduchess Maria Amalia (who also died in infancy).
According to the Mutual Pact of Succession the heir presumptive to the Habsburg realms was, at that moment, Charles’s niece, Archduchess Maria Josepha, who was followed in the line of succession by her younger sister, Archduchess Maria Amalia.
Four years before the birth of Archduchess Maria Theresa, faced with his lack of male heirs, Charles provided for a male-line succession failure with the Pragmatic Sanction of 1713.
The future Emperor Charles VI favoured his own daughters over those of his elder brother and predecessor, Joseph I, in the succession, ignoring the decree he had signed during the reign of his father, Leopold I.
The Mutual Pact of Succession was finally superseded
by the Pragmatic Sanction on April 9, 1713, the Emperor Charles VI announced the changes in a secret session of the council. The Pragmatic Sanction was to ensure the succession of Charles’s own daughters instead of Joseph.
The hereditary crowns belonging to the House of Habsburg were thus to be inherited by Charles’s elder surviving daughter, Archduchess Maria Theresa (born in 1717), rather than by Joseph’s elder daughter, Maria Josepha.

Empress Maria Theresa, Queen of Bohemia, Hungary, Croatia and Archduchess of Austria
Charles sought the other European powers’ approval. They demanded significant terms, among which were that Austria close the Ostend Company. In total, Great Britain, France, Saxony-Poland, the Dutch Republic, Spain, Venice, States of the Church, Prussia, Russia, Denmark, Savoy-Sardinia, Bavaria, and the Diet of the Holy Roman Empire recognised the sanction. France, Spain, Saxony-Poland, Bavaria and Prussia later reneged.
Since the hereditary Habsburg lands were under a Semi-Salic Law which excluded women from the inheritance until all male members of the Imperial House became extinct, this agreement required approval by the various Habsburg territories and the Imperial Diet.
The main reason for Saxony-Poland and Bavaria did not support the Pragmatic Sanction and instead still supported the Mutual Pact of Succession was due to the fact that the daughters of Emperor Joseph I, Archduchess Maria Josepha of Austria, married August III, King of Poland and Elector of Saxony (Friedrich August II) and
Archduchess Maria Amalia of Austria, married Elector Charles Albrecht of Bavaria, future Charles VII, Holy Roman Emperor.

Charles VII, Holy Roman Emperor
Prior to their respective marriages to Friedrich August II of Saxony (August III of Poland) and Charles Albrecht of Bavaria in 1719, both women were obliged to formally renounce their rights to the inheritance. Charles assumed the rivalry between Saxony and Bavaria would secure his daughter’s rights to the throne, since neither would be prepared to allow the other to inherit, but instead he gave his two greatest rivals a legitimate claim to the Habsburg lands.
Charles died in 1740, sparking the War of the Austrian Succession, which plagued his successor, Maria Theresa, for eight years.
The immediate cause of the war of the Austrian Succession was the death in 1740 of Emperor Charles VI (1685–1740) and the inheritance of the Habsburg Monarchy, often collectively referred to as Austria, by the Emperor’s daughter Archduchess Maria Theresa of Austria who became Queen Regnant of Hungary, Bohemia Croatia and Archduchess of Austria.
Marriage
The question of Maria Theresa’s marriage was raised early in her childhood. Leopold Clement of Lorraine was first considered to be the appropriate suitor, and he was supposed to visit Vienna and meet the Archduchess in 1723. These plans were forestalled by his death from smallpox that year.
Leopold Clement’s younger brother, François Étienne; (French, German: Franz Stefan) was invited to Vienna. Even though François Étienne was his favourite candidate for Maria Theresa’s hand, the Emperor Charles VI considered other possibilities.
Religious differences prevented him from arranging his daughter’s marriage to the Protestant Prince Friedrich of Prussia (future King Friedrich II of Prussia). In 1725, he betrothed her to Infante Carlos of Spain (future King Carlos III) and her sister, Infanta Maria Anna, to Infante Felipe of Spain and Duke of Parma. Other European powers compelled him to renounce the pact he had made with the Queen of Spain, Elisabeth Farnese. Maria Theresa, who had become close to François Étienne was relieved.

Franz Stefan, Holy Roman Emperor and Grand Duke of Tuscany
François Étienne remained at the imperial court until 1729, when he ascended the throne of Lorraine, but was not formally promised Maria Theresa’s hand until January 31, 1736, during the War of the Polish Succession.
King Louis XV of France and Navarre demanded that Maria Theresa’s fiancé surrender his ancestral Duchy of Lorraine to accommodate his father-in-law, Stanislaus I, who had been deposed as King of Poland.
In this arrangement François Étienne was to receive the Grand Duchy of Tuscany upon the death of childless Grand Duke Gian Gastone de’ Medici. The couple were married on February 12, 1736.
After her accession to the Habsburg hereditary domains Queen Maria Theresa dismissed the possibility that other countries might try to seize her territories and immediately started ensuring the imperial dignity for herself; since a woman could not be elected Holy Roman Empress, Maria Theresa wanted to secure the imperial office for her husband, but François Étienne did not possess enough land or rank within the Holy Roman Empire.
In order to make him eligible for the imperial throne and to enable him to vote in the imperial elections as elector of Bohemia (which she could not do because of her sex), Maria Theresa made François Étienne co-ruler of the Austrian and Bohemian lands on November 21, 1740.
It took more than a year for the Diet of Hungary to accept François Étienne as co-ruler, since they asserted that the sovereignty of Hungary could not be shared. Despite her love for him and his position as co-ruler, Maria Theresa never allowed her husband to decide matters of state and often dismissed him from council meetings when they disagreed.
During the War of the Austrian Succession, Charles Albrecht of Bavaria invaded Upper Austria in 1741 and planned to conquer Vienna, but his allied French troops under the Duc de Belle-Isle were instead redirected to Bohemia, and Prague was conquered in November 1741.
That meant that Charles Albrecht was crowned King of Bohemia in Prague on December 19, 1741, when the Habsburgs had not yet been defeated. He was unanimously elected “King of the Romans” on January 24, 1742 and became Holy Roman Emperor upon his coronation on 12 February 1742.

Maximilian III Joseph, Elector of Bavaria
Suffering severely from gout, Charles VII died at Nymphenburg Palace in January 1745. His brother Clemens August then again leaned towards Austria. After the decisive defeat in the Battle of Pfaffenhofen on April 15, Elector Maximilian III Joseph, son and heir of Emperor Charles VII (former Elector Charles Albrecht of Bavaria) quickly abandoned his imperial pretenses and made peace with Maria Theresa in the Treaty of Füssen, in which he agreed to support her husband, Grand Duke François Érienne of Tuscany, in the upcoming imperial election.
With the Treaty of Füssen, Austria recognized the legitimacy of Charles VII’s previous election as Holy Roman Emperor.
Also according to the Treaty of Füssen, Maria Theresa secured her husband’s election as Emperor, which took place on 13 September 1745. He succeeded Charles VII as Emperor Franz I Sefan.
Though Emperor Franz Stefan was well content to leave the wielding of power to his able wife, she was expected to cede power to her husband and later her eldest son, Emperor Joseph II, who were officially her co-rulers in Austria and Bohemia, Hungary and Croatia.
Empress Maria Theresa was the absolute sovereign who ruled with the counsel of her advisers. Maria Theresa promulgated institutional, financial, medical and educational reforms, with the assistance of Wenzel Anton of Kaunitz-Rietberg, Friedrich Wilhelm von Haugwitz and Gerard van Swieten.