The 1578 Battle of Alcácer Quibir is an interesting case of unintended consequences. The product of a Portuguese attempt to exploit a succession crisis in Morocco, its outcome actually helped create a succession crisis in Portugal. The situation in Morocco was a pretty straightforward usurpation. The Bani Zaydan, also known as the Saadis, were the dynasty that ruled either part or all of Morocco for about 100 years, gaining control over southern Morocco in the first half of the 16th century and then extending its dominion over all of Morocco through the first half of the 17th century. Under Muhammad al-Shaykh (d. 1557) they were able to eliminate both the Ottoman-backed Wattasid Dynasty of northern Morocco and the Portuguese colonial presence in coastal cities/fortresses like Agadir, Asilah, and the place where this battle was fought, al-Qasr al-Kabir (or Alcácer Quibir for the Portuguese).
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The Foreign Exchanges Companion 
Excellent bit of twine, sir, that ties together a nice bit of early modern history.
I know some Danes and I know some Portuguese, and neither takes kindly to being mistaken for a Swede/Spaniard. And, as it happens, my college girlfiend wrote her senior thesis on Nero – who evidently was more popular than American popular culture would have one believe, especially in the East – so she told me that Nero too was attached to a legend about RETURN HEROICALLY ONE DAY IN THE HOUR OF HIS PEOPLE’S GREATEST BLAH BLAH BLAH and that, for the next fifty years, con men of the appropriate age would appear out of the rising Sun to assert their claims.
Fun how the classics never go out of style.
The modern Turkish name for the city, İstanbul, derives from the Greek phrase eis tin polin (εἰς τὴν πόλιν), meaning “into the city” or “to the city”. This name was used in Turkish alongside Kostantiniyye, the more formal adaptation of the original Constantinople, during the period of Ottoman rule, while western languages mostly continued to refer to the city as Constantinople until the early 20th century. In 1928, the Turkish alphabet was changed from Arabic script to Latin script. After that, as part of the 1920s Turkification movement, Turkey started to urge other countries to use Turkish names for Turkish cities, instead of other transliterations to Latin script that had been used in the Ottoman times. In time the city came to be known as Istanbul and its variations in most world languages.
https://en.wikipedia.org/wiki/Constantinople
“Istanbul” or its Greek antecedents were used to refer to Constantinople informally for centuries before the Ottomans captured it. I’m talking about formal usage here, and the Ottomans retained Constantinople as the city’s formal name. “Istanbul” wasn’t widely used in formal, official contexts until the late 17th century, about 100 years after the events in question.