The state which developed in military and political aspects being established in south Dobruca breaking the resistance of Emperor Konstantinos the 4th by Asparuh, is most long-lasting the political organization established by Ogur Turks. We can understand that the state was founded on sound foundations because it could survive between two major powers such as Byzantium and Avar empires. Bulgar Turks from abroad came out successful in taking Slavic masses in the region under their control. The Bulgars, being unfamiliar with state idea, armed Slavs who used to live in tribe order and ensured their protecting themselves from Byzantium. The strictest political relations of Danube Bulgars were with Byzantium. Emperor Justinianus the 2nd, who married to Hazar princess, was ascended the throne for the second time in 705 with assistance of Bulgarian Khan Tervel (702-718). Emperor Philippikos' being overthrown in 713 is also considered as a result of Bulgarian advance in Byzantium territories. The force Bulgarian state gained in a short time can be understood from this event too. The Bulgarian helped Byzantium during Istanbul siege of Arabs in 717-718. Such cooperation brought about many financial interests to the Bulgarian state. However, Byzantium, taking advantage of the chaos in Bulgarian country in 8th century, organized various expeditions on Bulgarian territories. "Krum Khan" (803-814), who acceded to Bulgar throne in early 9th century, seized Hungary and Transylvania. Byzantine Emperor Nikepheros the 1st, being afraid of the "skillful warrior and intellectual organizer" personality of Krum, acted to get rid of him (811). He destroyed the capital city of the country Pereyaslav, now to the southwest of Şumnu (Shumen). However, in the end, Nikephoros was defeated, his army was routed, and he was killed at the battlefield. It was the first time a Byzantine emperor was killed by an enemy for 450 years. Krum Khan then defeated Mikhael the 2nd, who marched against the Bulgars commanding his army strengthened with units from eastern states of the empire, took an oath to hang his golden sparrow on the gilded Gate (the ceremony gate in Yedikule), by eliminating Byzantium. He occupied Sofia, Nis, and Belgrade city castles and thus took the greatest commercial and military transportation way between Europe and Middle East under control. He reached Edirne in 813 and leaving there under siege, went on proceeding. He besieged Istanbul in 814 Spring. However, he died instantly on 13 April 814 in the most impetuous moment of the attacks. His son Omurtag Khan (814-831) signed a commercial agreement of 30 years with Byzantium. Omurtag Khan, who wanted to agree also with Frankish Empire, could not be successful in that, and thus used his weapons and opened the saltpans for management again which were all closed after Roman Period, and thus earned for his state a great wealth. His period was the brightest period of Danube Bulgars. Constructed cities, palaces, constructions and improvements on a wide scale, aqueducts, monuments, developed cities and the epitaph and relief of Krum Han on horse on a high rock covering an area of 40 m2 are all the memories of that period. However, Bulgar Turks who were less in population (м.з. and culture) compared to the Slavs, began to be influenced by Slavic culture under Byzantine effect in time. The number of Slavs commissioned in civil service increased, the two societies mixed by means of marriages more and more, the influence of Slavic language grew and Turks began to get Slav rapidly. On Boris Khan's accepting Orthodox sect officially, the process of Bulgar's getting Slav came to an end.