Croatia Was Not an Orthodox Kingdom Waiting to Become Catholic. UsefulCharts Gets the History Wrong.
A king cannot convert a country to a church it already belongs to. Yet that is effectively the story UsefulCharts tells about medieval Croatia.
In Serbian & Croatian Monarchs Family Tree, presenter Jack Rackham offers an engaging tour of Balkan royalty, from medieval dynasties to the collapse of Yugoslavia. The family relationships are useful. The chronology is mostly recognizable. But when the video explains why Croatia became Catholic while Serbia remained Orthodox, it replaces a complicated historical relationship with a misleading conversion story.
The problem is not a missing date or an obscure king. It concerns one of the central distinctions between two neighboring countries whose religious histories remain important to their national identities.
And the surviving historical evidence tells a substantially different story.
Croatia Was Connected to Rome Long Before Krešimir IV
The video's most consequential assertion comes during its discussion of King Petar Krešimir IV, who ruled approximately from 1058 to 1074.
Rackham describes Croatia as a country that was largely Orthodox and credits Krešimir with fighting to impose Catholicism. His successor, Demetrius Zvonimir, supposedly completed the transformation.
It is a tidy explanation for why modern Croatia is predominantly Catholic.
It is also unsupported by the surviving evidence.
On June 7, 879, nearly two centuries before Krešimir's reign, Pope John VIII wrote to the Croatian ruler Branimir.
The pope informed Branimir that he had blessed the ruler, his people, his territory, and his government during a religious service at St. Peter's in Rome.
This was no isolated exchange.
A study by historian Mirjana Matijević Sokol, published by the Croatian cultural institution Matica hrvatska in 2018, examines a series of letters exchanged between the papacy and Croatian authorities.
The correspondence survives in an 11th-century copy of Pope John VIII's register, preserved in the Vatican's collections.
The letters establish something fundamental: Croatian political and religious authorities were communicating directly with Rome in the ninth century.
Branimir's government expressed loyalty to the Roman Church. The pope corresponded with Croatian clergy and addressed questions concerning episcopal appointments.
One letter concerned Theodosius, bishop-elect of Nin. The pope invited him to receive episcopal consecration from Rome.
Another addressed Croatian priests and their people, acknowledging their ruler's expression of loyalty to the Holy See.
These documents do not establish the religious affiliation of every inhabitant of ninth-century Croatia. They do, however, directly contradict any simple narrative in which Croatia had no substantial Roman ecclesiastical relationship until Krešimir imposed Catholicism nearly 200 years later.
The evidence is available in Matijević Sokol's study of Branimir's surviving correspondence.
The critical distinction is between a kingdom's ecclesiastical relationships and the religious beliefs of its entire population.
The video moves from one to the other without establishing the connection.
The Religious Conflict Was Not Simply Catholicism Against Orthodoxy
The video's explanation becomes still less convincing when examined against the church disputes of the 10th century.
In 925 and 928, ecclesiastical councils associated with Split addressed conflicts over church authority in Croatia and Dalmatia.
These controversies were not straightforward struggles to convert an Orthodox nation into a Catholic one.
They involved competing bishops, territorial jurisdiction, relations with Rome, and the use of different languages in Christian worship.
Historian Vadim Prozorov, writing in Early Medieval Europe in 2021, describes the conflict between the metropolitan church centered on Split and the bishopric of Nin.
The bishop of Nin sought greater ecclesiastical authority. The Dalmatian hierarchy sought to preserve its existing organization.
The resulting dispute concerned who would exercise authority over the church and its clergy.
It was a contest over jurisdiction, not evidence that Croatia's population was predominantly Orthodox.
Prozorov also identifies a significant limitation: the surviving acts of these early councils were transmitted through much later manuscripts, and their reliability requires critical examination.
That qualification matters. Medieval religious history cannot responsibly be reconstructed by treating every later account as an unquestionable record.
The video also overlooks the distinctive Croatian tradition of worship in Old Church Slavonic.
This is particularly damaging because language helps explain the religious controversies that the video misrepresents.
Croatian Christians used the Glagolitic script and celebrated parts of their liturgy in a Slavic language rather than Latin.
That did not automatically make them Eastern Orthodox.
The Old Church Slavonic liturgical tradition had received papal approval as early as 869, when Pope Adrian II authorized its use in the Roman rite.
The Croatian Old Church Slavonic tradition subsequently encountered opposition from church reformers seeking greater Latin-language uniformity.
The Old Church Slavonic Institute in Zagreb explains that Croatian clergy using the language faced accusations of heresy, while the underlying practice remained connected to the Roman liturgical tradition.
In 1248, Pope Innocent IV formally permitted the continuation of Croatian Glagolitic worship.
This is a far more revealing historical conflict than a supposed mass conversion from Orthodoxy to Catholicism.
It concerns religious authority, language, local identity, and the limits of uniformity within the Western Church.
Those struggles deserve explanation precisely because they complicate the modern assumption that different languages or scripts must indicate different denominations.
The Old Church Slavonic Institute's history of Glagolitic worship documents these distinctions.
There is another chronological problem.
The Great Schism of 1054 is conventionally associated with the separation of the Roman Catholic and Eastern Orthodox churches. But historians caution against treating it as a single moment when every Christian community instantly became a member of one of two clearly defined denominations.
Religious differences, jurisdictional disputes, and political competition developed over centuries.
A chapter in The Cambridge History of Christianity warns that interpreting earlier relations through the eventual schism can exaggerate divisions that contemporary participants did not necessarily recognize in the same way.
That warning applies directly here.
Calling Croatia an overwhelmingly Orthodox nation around the time of Krešimir IV imposes a modern religious classification on a medieval society without presenting the evidence needed to justify it.
What Krešimir IV Actually Did
There was a genuine religious reform movement during Krešimir's reign.
The video did not need to invent a conversion narrative to make that period interesting.
In 1060, Pope Nicholas II dispatched Cardinal Majnard to Croatia and Dalmatia.
The mission had both political and ecclesiastical dimensions.
According to the Croatian Biographical Lexicon, Majnard investigated allegations that Krešimir had been involved in the death of his brother Gojslav.
Krešimir denied involvement, swearing an oath alongside twelve regional nobles.
The papal representative subsequently confirmed his authority.
The same period saw church councils concerned with religious discipline, Latin-language worship, and reforms associated with Rome.
Prominent reformers included Archbishop Lawrence of Split, Bishop John of Trogir, and papal representatives.
Benedictine monasteries also played an important role. The biographical lexicon identifies at least seventeen major Benedictine monasteries within Krešimir's territories.
Krešimir supported monasteries through property donations, privileges, foundations, and royal protection.
These details establish a ruler actively connected to Western ecclesiastical institutions.
They do not establish that he converted a predominantly Orthodox population to Catholicism.
The distinction becomes especially important when the Croatian Encyclopedia addresses his involvement in efforts to restrict Slavic-language worship.
Its conclusion is cautious: Krešimir's precise position on those efforts is unknown.
The encyclopedia considers his support for religious reform plausible, based partly on his relationships with monasteries. But it does not present his alleged campaign against Slavic worship as an established fact.
That is a considerably narrower conclusion than the video's assertion that he fought to impose Catholicism on the kingdom.
The Croatian Encyclopedia's account of Krešimir IV and the Croatian Biographical Lexicon's detailed biography supply the relevant evidence.
There is a substantial historical story here about political legitimacy, papal influence, monastic wealth, and the gradual reshaping of religious institutions.
It is arguably more interesting than the explanation UsefulCharts provides.
A king accused of involvement in his brother's death, a papal investigation, powerful bishops, competing liturgical traditions, and substantial royal donations to monasteries offer enough material for a serious account of medieval religion and power.
Reducing that history to a king imposing Catholicism discards the very circumstances that would explain his conduct.
The Errors Extend Beyond Croatia
The religious account is the most significant problem, but it is not the only one.
The presentation also makes a straightforward chronological mistake concerning Montenegro.
While discussing Peter I of Serbia and his marriage to Princess Zorka, Rackham says Montenegro became a kingdom in the 19th century.
It did not.
Montenegro became an internationally recognized independent state in 1878, but its ruler, Nikola I, did not adopt the title of king until August 28, 1910.
New Zealand's Ministry for Culture and Heritage records Nikola's reign as king beginning on that date.
Princess Zorka married Peter Karađorđević in 1883 and died in 1890.
She therefore died twenty years before her father's principality became a kingdom.
The dynastic relationship is real. The chronology attached to it is wrong.
The Montenegrin Academy's dynastic encyclopedia establishes Zorka's dates, while New Zealand's official historical record confirms the kingdom's establishment in 1910.
This is a smaller mistake than the religious narrative.
Nevertheless, it is precisely the sort of error a royal-family history should avoid.
The video promises to explain how dynasties and royal titles developed. Whether a territory was a principality or kingdom at a particular moment is part of that explanation, not an incidental detail.
The Account of Yugoslavia's 1941 Coup Is Too Simple
A second substantial weakness appears near the end of the presentation.
The video describes how Yugoslavia's regency agreed to join the Axis powers during the Second World War.
A pro-British military coup then removed the regency, declared the young Peter II old enough to rule, and reversed Yugoslavia's position.
Rackham states that Yugoslavia backed out of the agreement before Germany invaded.
The implication is simple: Yugoslavia entered the Axis arrangement, the new government withdrew, and Hitler responded with invasion.
The surviving diplomatic record presents a more complicated sequence.
Yugoslavia signed the Tripartite Pact on March 25, 1941.
Two days later, military officers overthrew the government and displaced Prince Paul's regency.
The coup unmistakably changed the political situation.
But the new government did not simply announce an unambiguous withdrawal from the pact.
On March 28, General Dušan Simović met the American minister in Belgrade, Arthur Bliss Lane.
Lane's confidential telegram to Washington records Simović's explanation of the new government's position.
According to that report, the government did not wish to denounce the pact, but neither would it ratify it.
It considered the agreement the work of the previous administration and did not regard itself as bound by unratified provisions.
Simović also sought to avoid provoking Germany and Italy.
This was an unstable position, but it was not the straightforward diplomatic withdrawal described in the video.
The distinction matters because it changes our understanding of the crisis.
The new government was attempting to balance opposition to German domination against the immediate danger of invasion.
Hitler interpreted the coup as a hostile development and ordered military action.
Germany invaded Yugoslavia on April 6, 1941.
The coup was enormously consequential. But the diplomatic record does not support reducing the episode to a government simply leaving the Axis alliance.
The contemporary evidence is unusually strong because Lane's telegram survives in the United States government's published diplomatic records.
It can be examined directly in Foreign Relations of the United States, March 28, 1941.
Historian David A. T. Stafford's study of British involvement in the coup likewise notes that expectations of a clear repudiation of the pact were disappointed.
The more precise account does not excuse Hitler's invasion or diminish the coup's significance.
It simply restores the difference between a political revolution, an ambiguous diplomatic position, and a formal repudiation of an international agreement.
That distinction should survive even in a short educational video.
The Price of a Convenient Historical Explanation
UsefulCharts has a legitimate educational purpose.
Family trees can make complicated political histories easier to follow. Serbia's rival Obrenović and Karađorđević dynasties, its medieval Nemanjić rulers, and the transition from Serbian monarchy to Yugoslav monarchy are subjects particularly suited to visual explanation.
The video provides useful chronology and relationships.
Its most serious weakness appears when it goes beyond genealogy to explain why entire societies developed differently.
Croatia's Catholic identity and Serbia's Orthodox identity cannot be adequately explained by assigning the former to the determination of two medieval kings.
The available historical evidence places Croatian rulers in contact with Rome generations before Krešimir IV. It documents disputes over ecclesiastical jurisdiction and worship rather than a straightforward conversion of an Orthodox population.
It also leaves important questions about Krešimir's personal role unresolved.
The video's account converts uncertainty into certainty and substitutes a simple religious transformation for a much richer institutional history.
The mistakes concerning Montenegro and Yugoslavia show a related weakness: compression sometimes changes the facts rather than merely shortening their explanation.
These are not grounds for dismissing the entire presentation. Nor is there evidence that the creator deliberately distorted the history.
But accessibility is not an excuse for unsupported claims.
The danger of a clear, memorable historical explanation is that its mistakes can become just as memorable as its facts.
UsefulCharts succeeds at showing who inherited the crowns. It is considerably less reliable when explaining what those crowns changed.
That is the distinction viewers deserve to know.
References
1. UsefulCharts — Serbian & Croatian Monarchs Family Tree. Jack Rackham, UsefulCharts, publication date not independently confirmed.
Original video
The work under review supplies the claims concerning Croatia's religious transformation, Montenegro's royal status, and Yugoslavia's wartime alignment.
2. Mirjana Matijević Sokol — Pisana svjedočanstva o knezu Branimiru. Matica hrvatska, Hrvatska revija, 2018.
Read the study
Examines preserved papal correspondence documenting relations between Croatian authorities and Rome in the ninth century, including letters preserved in a later manuscript copy.
3. Vadim Prozorov — Ut primatum habeant: The Early Medieval Church in Dalmatia and the Aquileian Strategy. Early Medieval Europe, 2021.
Read the research
Establishes the importance of episcopal jurisdiction and competing church authorities in the disputes associated with Split and Nin.
4. Vadim Prozorov — The Tenth Century Councils in Split and the Problem of the Reliability of Their Acts. Church Studies, publication date not established from the consulted record.
Read the research
Explains why the councils' surviving documentation requires critical examination rather than unquestioning acceptance.
5. Kristijan Kuhar — Glagolitic Liturgy. Old Church Slavonic Institute, Zagreb, January 7, 2025.
Read the institutional history
Documents the Roman-rite context of Croatian Old Church Slavonic worship and the disputes over language that the video's conversion narrative obscures.
6. Petar Krešimir IV. Croatian Encyclopedia, Miroslav Krleža Institute of Lexicography, online edition.
Read the encyclopedia entry
Explicitly identifies uncertainty about Krešimir's position on church efforts to restrict Slavic-language worship.
7. Krešimir IV. Croatian Biographical Lexicon, Miroslav Krleža Institute of Lexicography.
Read the biography
Provides detailed evidence concerning the papal investigation, church reforms, Benedictine foundations, royal donations, and Krešimir's political relationships.
8. Latin and Greek Christians. The Cambridge History of Christianity, Cambridge University Press.
Read the chapter summary
Explains why the later Catholic–Orthodox division should not be projected backward as a fixed classification of earlier Christian communities.
9. Zorka Petrović Njegoš Karađorđević. Lexicon of Montenegrin Dynasties, Montenegrin Academy of Sciences and Arts.
Read the entry
Confirms Zorka's marriage in 1883 and death in 1890, establishing the chronology of her connection to the Serbian dynasty.
10. Kingdom of Montenegro. NZ History, New Zealand Ministry for Culture and Heritage.
Read the historical record
Confirms that Nikola I became king on August 28, 1910, correcting the video's placement of Montenegro's elevation in the 19th century.
11. Arthur Bliss Lane — Telegram to the United States Secretary of State, March 28, 1941. Foreign Relations of the United States, US Department of State.
Read the original diplomatic record
Records General Simović's explanation that his government would neither denounce nor ratify the Tripartite Pact, complicating the video's claim of an outright withdrawal.
12. David A. T. Stafford — SOE and British Involvement in the Belgrade Coup d'État of March 1941. Slavic Review, Cambridge University Press.
Read the scholarly analysis
Distinguishes the coup's anti-German political significance from the new government's failure to formally repudiate the Axis agreement.