The Union of the Two Sicilies and Greece
After King John II of Greece died suddenly in a riding accident, without issue, in 1858, his eldest sister, Theodora, ascended to the Greek throne. Though Theodora was fairly popular with the Greek people, her succession triggered a civil war that blossomed into the War of the Greek Succession, due to Theodora's marriage to King Francis II of the Two Sicilies; a large faction of Greeks refused to submit to another foreign King of a different religion, after their successful revolt against the Ottoman Empire and the establishment of the Kapodistrias dynasty as monarchs. Further, such a firm alliance between the Two Sicilies and Greece made the other Italian states uneasy, leading to open war, with the rebels and other Italian powers backing Theodora's younger sister, Sophia, who was married to the Russian Grand Duke Alexander, the second son of Emperor Alexander II.
Though Russian support for the Sophian faction was initially commanding, the beginning of the Polish Revolt of 1860 vastly reduced it, and by 1863 the Treaty of Syracuse was signed, with Sophia recognizing her sister's stronger claim. Theodora would rule Greece independently of her husband, and the treaty agreed that Greece and Two Sicilies would remain "permanently" separate nations, even when they would have the same monarch.
In the 20th century, the Greek/Sicilian bloc in the Mediterranean proved a solid middling power, defeating the Ottoman Empire in the Great War and establishing colonies in northern and central Africa. The Two Sicilies was the dominant partner in the union, but Greece remained independent in all its internal affairs.
In 1926, King Ferdinand III/I, after mass protests in Greece, created the Union Council, formally inviting the Greek parliament to recommend members to advise in questions of foreign affairs, and, in 1958, Queen Theodora I/II named the dual monarchy's first Greek head of government, who sat in and commanded a majority in the Greek parliament rather than the Sicilian, though by then party alignments in both countries were fairly well-developed, with the prime minister's deputies in Sicily commanding the majority there. Though the two nations are strictly independent of one another save on issues of foreign affairs, the union has slowly grown more statelike, most recently with the adoption of the Union Flag for use by civilian ships by King Michael in 2008, which has since been used in international deployment by joint Sicilian/Greek detachments under World Confederation missions in Africa and Asia.
The Union Flag below is based on an original design by a greater nationalist in the early 20th century, with Greek and pan-Italian colors symbolizing the union and cooperation of the Greek and Italian peoples in the union. When it was formally adopted for use by the modern union, the Royal Union Badge, which had been appended to the Greek and Sicilian flags in the 19th century to symbolize the union between them, was added to ward off the historically republican implications of the pan-Italian colors.