For centuries Byzantium’s influence over the Croats waxed and waned, first beginning in the early seventh century. Heraclius was the first emperor to enlist the aid of the Croats, to oust the troublesome Avars from Illyricum. Subsequently, the Croats were rewarded for expelling the Avars and settled by order of Heraclius into these lands (Illyricum). In time, the Croats would increasingly look to the Pope and steer away from Byzantium’s influence.
During the turn of the millennium 1000 AD, the Kingdom of Croatia co-existed between 3 European powers, the Holy Roman Empire, the Kingdom of Hungary (Magyars) and the Byzantine Empire. Croatia’s reign as a sovereign state during this period lasted nearly two centuries. It was, in fact, one of the most powerful kingdoms in the Balkans, a testimony of its existence amongst three empires.
Interestingly, despite the fact that most of its history would be politically ruled by others, no one could begrudge them of their will for self termination and independence. 1000 AD Croatia shared fairly good relations with the Pope and the Byzantine Emperor Basil II and later Constantine VIII. However, by 1102 AD Croatia’s crown would pass into the hands of the Hungarian dynasty. Its dream of full independence wouldn’t be realised again until the twentieth century.
Though, if we look back to the year 926 AD, at a time when the age of empire attempted to dominate many different ethnic and national groups, the newly recognised Kingdom of Croatia flourished for a while under its first king Tomislav, but faced possibly its greatest threat very early on in its quest to remain an autonomous kingdom. This threat came in the form of a Bulgarian Tsar and this is the story I would like to briefly focus on.
Simeon I of Bulgaria 893-927 AD.
The Bulgarian who caused the Croats the greatest of concern was Tsar Simeon. He was a ruler who struck fear into the heart of most people living in the Balkans, especially the Serbs, whom he had completely destroyed through a series of successful campaigns. (In destroying Serbia, he pushed a large number of expelled Serbs into Croatia.) But more importantly he also harboured dreams of destroying the Byzantines and making himself Emperor of the Romans. Though, as hard as he tried militarily and politically, the Byzantines doggedly held on to their empire.
Frustrated, Simeon shifted his attention once again (after defeating the Serbs) to expanding his stranglehold on the Balkans, by pushing even further west as far as the Croatian border. If he could defeat the militarist kingdom of Croatia, he thought it would open up an opportunity, possibly one last time before his death to try and conquer the Byzantines. By knocking out the Croats, whom were on friendly terms with the Byzantines, he hoped he would weaken the Byzantines resolve to defy him.
Interestingly, so as long as Simeon was ruler of the Bulgars, the Byzantines would remain on high alert of Simeon’s imperial and territorial ambitions. To placate the Tsar, the Byzantines payed him a handsome annual subsidy to stay clear of Byzantine Imperial territory. But importantly, they also sort the help of King Tomislav, the first Croatian king, as a kind of ‘get out of trouble’ clause, obviously in case things went pear-shaped with Simeon.
In previous campaign, the Croats were more than willing to come to the aid of the Emperor. In Italy, for example, the Croats evidently sent their own troops to expel Muslims from the Byzantine held city of Sipontus, in the Byzantine province of Langobardia. Apparently all this was possible because the Byzantine emperor Romanus Lecapenus had won Tomislav’s friendship in the 920’s. (The Croats loyalty may have been one of many reasons why Romanus had handed Tomislav Byzantine dalmatia and recognising him as King? That said, there is also some conjecture about who recognised Tomislav first. Was it Pope John X in 925 or Romanus?)
King Tomislav of Croatia 925-928.
When Simeon found out that he had been undermined by the Croats (for their determined insistence in protecting the Serbs), and fearing an attack from an alliance between the Byzantine Emperor and Tomislav, he angrily decided to attack the Kingdom of Croatia in a pitched battle to teach them a lesson.
This pitched battle was fought in the Bosnian highlands in 926, with strength numbers on both sides disputed, possibly estimated in the tens of thousands. As the battle began to unfold, Tomislav had strategically chosen the mountainous battlefield of the highlands to work to his favor, leaving Simeon unaware of the strength of the Croats (and their skill in battle). In the ensuing confrontation the Croats utterly crushed the Bulgarians with their field army and cavalry. Simeon would subsequently never recover from this blow and would die a year later from a heart attack. It would take Bulgaria 50 years to recover from the humiliating defeat and Simeon’s death would readdress the balance of power in the Balkans peninsula.
The Croats would eventually abandon their alliance with Byzantium, for fear of retaliation from the Bulgars. They likely believed it was their best bet for survival in helping them retain their independence and sovereignty? Whatever the reason, the Croats would remain fiercely independently as a nation for almost the next two hundred years, until its union with Hungary in 1102 AD.
Rearview Mirror 
Warfare is a fascinating subject. Despite the dubious morality of using violence to achieve personal or political aims. It remains that conflict has been used to do just that throughout recorded history.
Your article is very well done, a good read.