The Austro-Hungarian Compromise of 1867
The Austro-Hungarian Compromise of 1867 was an agreement reached by Austria and Hungary on 8 February, 1867. This agreement regulated the relations between the two nations and established the Dual Monarchy of Austria-Hungary. The kingdom of Hungary had desired equal status with the Austrian Empire, which was weakened by its defeat in the Austro-Prussian war of 1866 and the economic recession that followed. The Austrian emperor Francis Joseph gave Hungarians full internal autonomy, which they enjoyed in the period before 1848. In 1848 the Hungarians revolted against the Austrians (more here), but their revolution failed and a military dictatorship was instituted over them. In return Hungary agreed that the empire should still be a single great state for purposes of war and foreign affairs, thus maintaining its dynastic prestige abroad. The Dual Monarchy lasted until the end of the First World War in 1918, when Austria-Hungary was dissolved after its defeat. This article will briefly discuss the reasons for the compromise, some of its important terms and its impact afterwards (Britannica, 2022).

Until 1848
In 1804, Francis II assumed the title of Emperor of Austria and of all the lands that the Habsburgs had ruled over, including Hungary. Hungary formally became part of the Empire of Austria. The Hungarian legal and judicial system remained separate and independent from that of the Austrian Empire. The administration and the structures of central government of the Kingdom of Hungary also remained separate from the Austrian administration and Austrian government until the Hungarian revolution of 1848. Ιn Hungary, the coronation was absolutely indispensable, in order for a monarch to be considered legitimate. Therefore, the Habsburg monarchs of Austria had to be crowned as Kings of Hungary in order to exercise their royal prerogatives in the Kingdom. For that purpose, after the agreement has been signed, Franz Joseph was crowned King of Hungary on 8th June, 1867, in Buda.
The Military Dictatorship
In March 1849 an imperial proclamation was issued by the emperor Francis Joseph, establishing a united constitution for the whole empire. According to the new proclamation, the traditional territorial integrity of Kingdom of Hungary would be terminated and carved up. The Austrian government pursued a radically new imperial policy. It wanted to develop a unified solid empire in the spirit of the imperial constitution. The new constitution of Austria provided absolute power for the monarch in all Habsburg-ruled territories. It also went against the historical constitution of Hungary and tried to nullify it.
In the failed Hungarian Revolution of 1848, the Hungarians came close to ending ties with the Habsburg Dynasty but were defeated by the Austrian Empire only after the military intervention of the Russian Empire. After the restoration of Habsburg power, Hungary was placed under martial law. A military dictatorship was created in Hungary. Every aspect of Hungarian life would be put under close scrutiny and governmental control. Hungary became officially part of the unified Austrian Empire in October 1851. In addition, the Kingdom of Hungary lost its own customs borders (Berstein & Milza, 1992/1997).

Crisis Within Austria
In the period before 1867, the Austrian Empire faced problems that meant that compromise with the Hungarians appeared to be their only viable option. In 1866, Austria was completely defeated in the Austro-Prussian War. Its position as the leading state of Germany ended. However, Bismarck did not intend to humiliate Austria and offered it favorable terms. In fact, it is not unlikely that the compromise between Austria and Hungary was Bismarck's own idea (more about Bismarck here). As a consequence, the Habsburg Empire was on the verge of collapse in 1866, as the war caused a financial crisis. The Habsburgs were forced to reconcile with Hungary, to save their empire and dynasty.
Terms of the Compromise
Thus, a dual monarchy of Austria-Hungary was established. The Kingdom of Hungary was separate from, but no longer subject to, the Austrian Empire. The territorial integrity of the Kingdom of Hungary was restored. The agreement also restored the old historic constitution of the Kingdom of Hungary. The lands of the House of Habsburg were reorganized as a real union between the Austrian Empire and the Kingdom of Hungary. The monarch reigned as Emperor of Austria in the Austrian half of the empire, and as King of Hungary in Kingdom of Hungary. The Cisleithanian (Austrian) and Transleithanian (Hungarian) states were governed by separate parliaments and prime ministers. The two countries conducted unified foreign diplomatic and defense policies. For these purposes, common ministries of foreign affairs, defense and their expenditures were maintained. The relationship of Hungary to Austria was reduced to partnership in a real union.
Under the Compromise, the Hungarian parliament was re-established. The Hungarian legal and judicial system and its laws were restored in the territory of the Kingdom of Hungary. All common decisions had to be ratified by the Austrian parliament to be valid on Austrian territory, and by the Hungarian parliament to be valid on the Hungarian territory. There was no common citizenship in Austria–Hungary. One citizen was either Austrian or Hungarian, never both. Despite Austria and Hungary sharing a common currency, they were economically sovereign and independent entities. A common Austro-Hungarian war ministry was formed immediately for the common armed forces. The Emperor-King was absolute head of the army. He appointed the senior officials, had the right to declare war and state of emergency, and was the commander of the army (Lindemann, 2012/2014).

Conclusion
With a territory of more than 675,000 square kilometres and a population of more than 50 million, the newly formed Austria-Hungary was one of the largest empires in Europe at the end of 19th century and the beginning of the 20th. More than a dozen nationalities lived in its territory, including Germans, Hungarians, Serbs, Croats, Bosnians, Slovenes, Romanians, Ukrainians, Poles, Czechs, Slovaks, Italians, Jews, etc.
The compromise and its consequences were not universally accepted. For example, many Hungarians did not accept it, as it did not meet their national aspirations for an independent Hungarian state. However, it was a treaty that simultaneously saved, albeit temporarily, the Austrian Empire and made the Hungarian nation a political entity. Despite all the tensions and conflicts, the Austro-Hungarian Monarchy provided with peace, economic progress, social stability, and cultural blooming its multi-ethnic population for decades until its collapse in 1918 (Szekely, 2015).
References
Berstein, S. & Milza, P. (1997). History of Europe, the European Agreement and the Europe of Nations 1815-1919, (A. K. Dimitrakopoulos, Trans.). Athens: Alexandria (Original work published 1992). pp. 141-146.
Britannica, T. Editors of Encyclopaedia (2022, February 1). Ausgleich. Encyclopedia Britannica. Retrieved from: https://www.britannica.com/event/Ausgleich and https://www.britannica.com/place/Hungary/The-Dual-Monarchy-1867-1918
Lindemann, A. S. (2014). A History of Modern Europe - From 1815 to the Present. (G. Christidis Trans.). Athens: Kritiki. (Original work published 2012). pp. 169-174.
Szekely, T. (2015, July 28). On This Day – In 1867 Hungary Establishes Dual Monarchy With Austria, hungarytoday.hu. Retrieved from: https://hungarytoday.hu/day-1867-hungary-austria-establish-dual-monarchy-67321/
Image Sources
Engerth, E. (ca 19th Century). Coronation of Emperor Franz Joseph and Empress Elisabeth of Austria as King and Queen of Hungary, on June 8th, 1867, in Buda, Capital of Hungary. [Painting]. Retrieved from: https://commons.wikimedia.org/wiki/File:Ferenc_J%C3%B3zsef_koron%C3%A1z%C3%A1sa_Bud%C3%A1n.jpg
Unknown. Coat of Arms of Austria-Hungary. Retrieved from: https://hungarytoday.hu/day-1867-hungary-austria-establish-dual-monarchy-67321/
Unknown. The map of Cisleithanian and Transleithanian after the Austro-Hungarian compromise of 1867. Retrieved from: https://commons.wikimedia.org/wiki/File:Cisleithanien_Transleithanien.png