There was a period of time when the Greece 's western islands (usually called "Ionian islands") were devastated by the Middle Ages invasions and wars and so lost most of their original greek population: not only the island of Corfu (the greek "Kerkyra") seemed to be dominated by the nearby Italians (who largely colonised the island after the year 1100 AD) and so would be forever italian (or italianised, because the area was and is greek), but also -in minor proportions- the islands of Cefalonia ("Kephalonia"), Itaca ("Ithaca") and Zante ("Zakynthos").
Greece in 1388 AD. Note that Venice possessed Corfu and Creta, while Florence the Attica region around Athens and the other Ionian islands were in the "County Palatine of Cefalonia".
The Ionian islands remained under Byzantine rule after the end of the Roman empire, before being caught up in the wars of powerful European families (mainly Italian and French). Zante, Cefalonia and some of the smaller islands were conquered by the Normans of southern Italy in the 12th Century. Indeed from the late 11th century, the Ionian Islands became a battleground in the "Byzantine–Norman" Wars. The island of Corfu was held by the Normans in 1081–1085 and 1147–1149, while the Venetians unsuccessfully besieged it in 1122–1123. The island of Cephalonia was also unsuccessfully besieged in 1085 AD, but was plundered in 1099 AD by the Pisans and in 1126 AD by the Venetians. Finally, Corfu and the rest of its byzantine theme except for Leucas were captured by the Normans under Guglielmo II of Sicily in 1185 AD.
Although Corfu was recovered by the Byzantines by 1191 AD, the other islands henceforth remained lost to Byzantium, and formed a "County Palatine of Cephalonia and Zakynthos" under the sicilian admiral Margaritus of Brindisi. The County Palatine of Cephalonia and Zakynthos existed for four centuries, from 1185 to 1479 AD as part of the Kingdom of Sicily. It is noteworty to pinpoint that the title and the right to rule the Ionian islands of Cephalonia and Zakynthos was originally given to the italian Margaritus of Brindisi for his services to Guglielmo (William) II, King of Sicily, in 1185 AD. He ordered many of his sailors to move from southern Italy (mainly from Brindisi) to the Ionian islands with their families, in order to control better this territory.
In 1267 AD, Charles of Anjou, French King of Sicily, took the island of Corfu and attempted to replace the existing Orthodox religion with the Catholic one. Orthodox Christians were persecuted and all churches converted to Catholic churches. Many colonists from catholic Italy moved to the island, starting the ethnic group now called "Italian Corfiots" and located mainly in Corfu city. But the attempt of conversion fell and Corfu returned under Venetian rule in 1386 AD. Corfu stayed under Venetian domination for a long period of more than four centuries until 1797 AD, during which a large number of buildings, monuments, and other constructions were built becoming the symbols of Venetian/Italian architecture in Greece.
The italian Tocco family conquests & possessions in the Ionian islands in the XIV century
The County Palatine was governed by three families (who moved some families from Italy and France to repopulate the Ionian islands): the italian Orsini, the french House of Anjou and the italian Tocco family. The rule of the family of Tocco lasted for 122 years, up until 1479, when Ottomans captured Cephalonia, Zante, Lefkada and Ithaca.
However the Turkish rule in the three islands of Cephalonia, Zante and Ithaca was short-lived. In 1481 AD, two years after the beginning of the Turkish rule, Antonio Tocco invaded and briefly occupied Cephalonia and Zante but he was soon driven out by the Venetians. Zante was officially recovered by the Venetians in 1485 AD. Then, Cephalonia, after sixteen years of Turkish occupation (1484–1500), became part of the "Stato da Màr" of the republic of Venice on 24 December 1500, with the Siege of the Castle of St. George. Finally, Ithaca, following the fate of Cephalonia, was conquered by Venice in 1503.
After Venice captured Cephalonia on 24 December 1500, the administration of the defense of all the islands was delegated to an official seated in Corfu. This official was being referred to as "the General Provveditore of the Three Islands" ("Provveditore Generale delle Tre Isole") and resided at the fortress of Angelokastro from 1387 AD to the end of the 16th century. The Three Islands refer to Corfu, Zante and Cephalonia. The Venetian equivalent for "Ionian Islands" is "Ixołe Jonie", the Italian being "Isole Ionie".
We know that before the XIV century the island of Corfu was populated by greek speaking inhabitants in the country & the villages, however the capital (Corfu city) was nearly fully venetian speaking. But this changed when the Turks wanted to conquest the island: the Ottomans in 1537 AD were not able to conquer the capital (and so most of the venetian speaking citizens survived the war) but did terrible massacres in the island's hinterland - while deporting as slaves nearly all of the christians living there (some estimates are terrible: the enslaved were more than 22,000 and so the Greeks of Corfu were reduced to a minimum of survivers).
Italian Tocco family's Coat of Arms, when ruled the "County Palatine of Cephalonia & Zante"
As a consequence of these Ottoman attacks & huge enslavements (that were done not only with Corfu, but also with all the other Ionian islansds) when the central Ionian Islands were captured by Venice their population was very low and Ithaca was completely uninhabited. To address this problem, a small colonisation to the islands took place. Catholic Italians from Italian "Terraferma" (and a few Corfiot Italians from Corfu) with some Orthodox Greeks from the "Stato da Màr" were transferred to the islands as part of the colonisation. The phenomenon is well attested for Cephalonia, after whose conquest in 1500 AD the island was colonized not only by civilian but also by military (called "Stradioti") refugees from the lost Venetian fortresses of Modon and Coron. Furthermore the island also received an influx of Italan families from the Venetian-ruled island of Crete, just conquered by the Turks.
Venetians, being Catholics, retained the privileges enjoyed by the Latin bishopric of the islands under the Count Palatine dynasties. The Catholics were not numerous, and during the Venetian period, they were mainly concentrated in Corfu, Itaca and Cephalonia. Most of them were descendants of Italian settlers but there were some conversions by Greeks to Catholicism.
After the terrible 3 tentatives of the Ottomans to conquer Corfu the researchers Mancini & D'Ambrosio think that in the 1580 census nearly 80% of the island inhabitants were venetian speaking and catholic, concentrated in Corfu city - while the other areas of Corfu were nearly totally depopulated. Something similar happened after the occupations of the other Ionian islands by the Turks: probably in those years Cephalonia had 2/3 of the population that was venetian speaking and catholic, while Itaca had a something similar percentage (but Zante had only around 35% of "italianised" inhabitants). So, we can say that these 3 islands (Corfu, Cefalonia and Itaca) were italianised at the end of the "Cinquecento" (at least we can say: more or less -because, of course, we have no precise statistical data about).
POSSIBLE POPULATION -according to "Paparrigopoulos, Constantine (1860). History of the Greek Nation, XI"- in 1580 in the islands of:
1) Corfu/Kerkyra................ (16000, of which 14000 venetian speaking)
2) Cefalonia/Kephalonia... (18000, of which 13500 " )
3) Itaca/Ithaca ................... (300, of which 250 " )
4) Zante/Zakynthos.......... .(14000, of which 4500 " )
Nota Bene: At least half of the venetian speaking population in Cefalonia and Zante was bilingual (greek-venetian), meaning they were Greeks partially "italianised" (or were descendants from at least one Italian relative, like a grandfather).
But the Republic of Venice welcame -after the Ottoman attacks & conquests in the XVI century- many refugees from the continental Greece conquered by the moslem Ottomans and so the islands were soon "flooded" by Greek christians. As a consequence when the republic of Venice ended in 1797 AD the orthodox Greeks were the majority in all the Ionian islands, with the only exception in Corfu city.
For example, after the collapse of the "Hexamilion wall", which was supposed to act as a defense across the Isthmus of Corinth; and hence, protect the Peloponnese, Leonardo III Tocco made an agreement with Venice to accept 10,000 refugees from this region. Leonardo III Tocco and his realm was increasingly vulnerable from Ottoman Turkish attacks. These refugees consisted of Greeks, Arvanites/Albanians and some Venetian officials & administrators (many with their families) and most of them were settled in Zante & Leucada. However Zakynthos was captured by the Ottoman Empire in 1478 AD, but conquered by the Republic of Venice in 1482 AD and remained for 3 centuries free of the Turk domination while mostly greek populated.
In the last two centuries of Venice domination of the Ionian islands, the greek speaking inhabitants grew in percentage, while the venetian/italian speaking diminished, remaining only in the upper class categories, related to military and administrive control. But with the weakening of the Republic of Venice, many italian speaking families preferred to go back to the italian peninsula to live without the danger of Ottoman attacks or conquests.
Only in Corfu city this reduction was minimal (one worldwide famous Corfiot Italian was Felice Beato, photographer born in Corfu city -or Venice, according to a few historians- in 1833: see photo of him in 1866 to the left)
The years when the Ionian islands were "italian" or "italianised" were over forever.....even if the italian irredentism (note that Ugo Foscolo -one of the Italian Risorgimento fathers- was born in Zante) appeared powerful during Mussolini's rule in the late 1930s/early 1940s.
if interested about these fascism years, please read my "Corfu italiana" (https://researchomnia.blogspot.com/2024/04/).