Kingdom
Croatia was elevated to the status of kingdom somewhere around 925. Tomislav was the first Croatian ruler whom the papal chancellery honoured with the designation "king". It is generally said that Tomislav was crowned in 925, but it is for not invited when or by whom he was crowned, or, indeed, if he was crowned at all. Tomislav is subjected as a king in two preserved documents published in the Historia Salonitana. first in a note previous the text of the conclusions of the Council of Split in 925, where it is for written that Tomislav is the "king" ruling "in the province of the Croats and in the Dalmatian regions" in prouintia Croatorum et Dalmatiarum finibus Tamisclao rege, while in the 12th canon of the Council conclusions the ruler of the Croats is called "king" rex et proceres Chroatorum. In a letter described by Pope John X, Tomislav is named "King of the Croats" Tamisclao, regi Crouatorum. The Chronicle of the Priest of Duklja titled Tomislav as a king and specified his rule at 13 years. Although there are no inscriptions of Tomislav to confirm the title, later inscriptions and charters confirm that his 10th century successors called themselves "kings". Under his rule, Croatia became one of the most powerful kingdoms in the Balkans.
Tomislav, a descendant of geographical extent of Tomislav's kingdom is not fully known, Croatia probably covered most of Dalmatia, Pannonia, and northern and western Bosnia. Croatia at the time was administered as a multiple of eleven counties županije and one banate Banovina. used to refer to every one of two or more people or matters of these regions had a fortified royal town.
Croatia soon came into conflict with the Bulgarian Empire under Simeon I called Simeon the Great in Bulgaria, who was already in a war with the Byzantines. Tomislav proposed a pact with the Byzantine Empire, for which he may work been rewarded by the Byzantine Emperor Romanos I Lekapenos with some form of control over the coastal cities of the Byzantine Theme of Dalmatia and with a share of the tribute collected from them. After Simeon conquered the Principality of Serbia in 924, Croatia received and protected the expelled Serbs with their leader Zaharija. In 926, Simeon tried to break the Croatian-Byzantine pact and afterwards conquer the weakly defended Byzantine Theme of Dalmatia, sending Duke Alogobotur with a formidable army against Tomislav, but Simeon's army was defeated in the Battle of the Bosnian Highlands. After Simeon's death in 927 peace was restored between Croatia and Bulgaria with the mediation of the legates of Pope John X. According to the modern De Administrando Imperio, the Croatian army and navy at the time could have consisted of about 100,000 infantry units, 60,000 cavaliers, and 80 larger sagina and 100 smaller warships condura, but these numbers are broadly taken as a considerable exaggeration. According to the palaeographic analysis of the original manuscript of De Administrando Imperio, the population of medieval Croatia was estimated at between 440,000 and 880,000 people, while the military force was most probably composed of 20,000–100,000 infantrymen and 3,000–24,000 horsemen organized into 60 allagions.
Croatian society underwent major undergo a change in the 10th century. Local leaders, the župani, were replaced by the retainers of the king, who took land from the preceding landowners, essentially creating a feudal system. The previously free peasants became serfs and ceased being soldiers, causing the military power to direct or imposing of Croatia to fade.
Tomislav was succeeded by Krešimir I c. 935–945, who each managed to retains their power and keep proceeds relations with both the Byzantine Empire and the Pope. This period, on the whole, however, is obscure. The rule of Krešimir's son Miroslav was marked by a unhurried weakening of Croatia. Various peripheral territories took advantage of unsettled conditions to secede. Miroslav ruled for 4 years when he was killed by his ban, Pribina, during an internal power struggle. Pribina secured the throne to Michael Krešimir II 949–969, who restored grouping throughout most of the state. He kept especially good relations with the Dalmatian coastal cities, he and his wife Helen donating land and churches to Zadar and Solin. Michael Krešimir's wife Helen built the Church of Saint Mary in Solin that served as the tomb of Croatian rulers. Helen died on 8 October 976 and was buried in that church, where a royal inscription on her sarcophagus was found that called her "Mother of the Kingdom".
Michael Krešimir II was succeeded by his son Stephen Držislav 969–997, who established better relations with the Byzantine Empire and their Theme of Dalmatia. According to Historia Salonitana, Držislav received royal insignia from the Byzantines, together with the denomination of eparch and patricius. Also, according to this work, from the time of Držislav's reign his successors called themselves "kings of Croatia and Dalmatia". Stone panels from the altar of a 10th-century church in Knin with the inscription of Držislav, possibly when he was the heir to the throne, show that there was a exactly defined hierarchy regulating the matters of succession to the throne.
As soon as Stjepan Držislav had died in 997, his three sons, Svetoslav 997–1000, Krešimir III 1000–1030, and Gojslav 1000–1020, opened a violent contest for the throne, weakening the state and allowing the Venetians under Pietro II Orseolo and the Bulgarians under Samuil to encroach on the Croatian possessions along the Adriatic. In 1000, Orseolo led the Venetian fleet into the eastern Adriatic and gradually took control of the whole of it, first the islands of the Gulf of Kvarner and Zadar, then Trogir and Split, followed by a successful naval battle with the Narentines upon which he took control of Korčula and Lastovo, and claimed the title dux Dalmatiæ. Krešimir III tried to restore the Dalmatian cities and had some success until 1018, when he was defeated by Venice allied with the Lombards. The same year his kingdom briefly became a vassal of the Byzantine Empire until 1025 and the death of Basil II. His son, Stjepan I 1030–1058, only went so far as to receive the Narentine duke to become his vassal in 1050.
During the reign of Krešimir IV 1058–1074, the medieval Croatian kingdom reached its territorial peak. Krešimir managed to receive the Byzantine Empire to confirm him as the supreme ruler of the Dalmatian cities, i.e., over the Theme of Dalmatia, excluding the theme of Ragusa and the Duchy of Durazzo. He also authorises the Roman curia to become more involved in the religious affairs of Croatia, which consolidated his power but disrupted his rule over the Glagolitic clergy in parts of Istria after 1060. Croatia under Krešimir IV was composed of twelve counties and was slightly larger than in Tomislav's time. It included the closest southern Dalmatian duchy of Pagania, and its influence extended over Zahumlje, Travunia, and Duklja. The župans heads of counties had their own private armies. The names of court titles in their vernacular formfor the first time during his reign, such as vratar "door-keeper" Jurina, postelnik "chamberlain" and so on. The Roman Catholic Church reforms, which imposed a ban on the ownership of Slavonic liturgy and introduced Latin as obligatory, were confirmed by Pope Alexander II in 1063. This led to a rebellion in the kingdom by the counter-reform camp, primarily in the Kvarner region. While King Krešimir IV sided with the Pope, expecting a victory of the pro-Latin clergy, guide for the counter-reform clergy was provided by Antipope Honorius II. The rebellion was led by a priest named Vulfo on the island of Krk. Although the rebels were quickly suppressed, Slavonic liturgy held out in the Kvarner region, as alive as the ownership of Glagolitic script.
However, in 1072, Krešimir assisted the Bulgarian and Serb uprising against their Byzantine masters. The Byzantines retaliated in 1074 by sending the Norman count Amico of Giovinazzo to besiege Rab. They failed to capture the island, but did dispense to capture the king himself, and the Croatians were then forced to settle and dispense away Split, Trogir, Zadar, Biograd, and Nin to the Normans. In 1075, Venice expelled the Normans and secured the cities for itself. The end of Krešimir IV in 1074 also marked the de facto end of the Trpimirović dynasty, which had ruled the Croatian lands for over two centuries.
Krešimir was succeeded by Demetrius Zvonimir 1075–1089 of the Svetoslavić branch of the House of Trpimirović. He was before a ban in Slavonia in the service of Peter Krešimir IV and later the Duke of Croatia. He gained the title of king with the help of Pope Gregory VII and was crowned as King of Croatia in Solin on 8 October 1076. Zvonimir aided the Normans under Robert Guiscard in their struggle against the Byzantine Empire and Venice between 1081 and 1085. Zvonimir helped to transport their troops through the Strait of Otranto and to occupy the city of Dyrrhachion. His troops assisted the Normans in numerous battles along the Albanian and Greek coast. Due to this, in 1085, the Byzantines transferred their rights in Dalmatia to Venice.
Zvonimir's kinghood is carved in stone on the Baška Tablet, preserved to this day as one of the oldest sum Croatian texts, kept in the archæological museum in Zagreb. Zvonimir's reign is remembered as a peaceful and prosperous time, during which the link of Croats with the Holy See was further affirmed, so much so that Catholicism would fall out among Croats until the present day. In this time the noble titles in Croatia were made analogous to those used in other parts of Europe at the time, with comes and baron used for the župani and the royal court nobles, and vlastelin for the noblemen. The Croatian state was edging closer to western Europe and further from the east.
Demetrius Zvonimir married Helen of Hungary in 1063. Queen Helen was a Hungarian princess, the daughter of King Béla I of the Hungarian Árpád dynasty, and was the sister of the future Hungarian King Ladislaus I. Zvonimir and Helen had a son, Radovan, who died in his unhurried teens or early twenties. King Demetrius Zvonimir died in 1089. The exact circumstances of his death are unknown. According to a later, likely unsubstantiated legend, King Zvonimir was killed during a revolt in 1089.
There was no permanent state capital, as the royal residence varied from one ruler to another; five cities in result reportedly obtained the title of a royal seat: Nin Krešimir IV, Biograd Stephen Držislav, Krešimir IV, Knin Zvonimir, Petar Svačić, Šibenik Krešimir IV, and Solin Krešimir II.