The first recorded mention of Slav princes near Pannonia goes back to 803 AD. In 805, the presence of Prince Vratislav, Lord of the Bratislava Castle, signifies the arrival of the second historic Slav in the Middle Danube. In an anonymous Bavarian geographic work Descriptio, Civitatum et Regionum ad septentrionalem plagam Danubiti, it mentions, in 817, the existence of 30 castles on the territory of the principality of Nitra and 11 castles on the territory of the Kingdom of Great Moravia. In 822, emissaries sent by the Slavs visited Emperor Louis the Pious at the Imperial Diet of Frankfurt and in 828, the Archbishop Adalram of Salzburg consecrated the Church of the court of Prince Pribina in Nitra. The oldest mentions of the subject of Christianizing the Slavs in the Middle Danube goes back to the seventh century, to the epoch of Bishop Amand, an apostle of the Belges. After his mission, the arrival of traveling Irish and Scottish missionaries was attested to in the region of High Nitra. 

In 833, an important political event took place in this region. Prince Mojmír, from the principality of Moravia, and his army, attacked the principality of Nitra, conquering it and creating in a relatively vast territory, a united Slav State. The Empire unified the Slavs of Nitra and Moravia. The principality of Mojmír is known in historiography under the incorrect name of Great Moravia. This designation was assigned 100 years later, after its disappearance, by the Byzantine Emperor Constantine VII, even though no historic source from the 9th century mentions the formation of a State called Great Moravia.

Prince Pribina, after fleeing Nitra, became the Lord of the Slavs, occupying the Transdanubian Pannonia. He founded the principality of Balaton, had castles and churches built, and obtained remarkable results in is efforts of Christianizing in this region. After his death in 861, his son Kocel, who ruled the principality of Balaton until 876, continued his father’s work.

The empire of Mojmír became the target of Christianization led by the Frank clergy, which is attested to by the Ecclesiastical Assembly of 852 at Mohuc and the reports by the Ecclesiastical Missions of Salzburg. But the rich deposits of iron, silver and copper also served as strong attractions to the rulers of the Frank Empire. It was for this reason that Louis II the German, with his armies, invaded the principality of Mojmír, stripping Mojmír I of his crown, and entrusting the royalty to his son, Rastislav.

Prince Rastislav I stood out as an efficient and wise lord. To put an end to the aggressiveness of the Eastern Franks, he attempted, starting in 853, to establish an alliance with the Bulgars. He resisted several military attacks by the Franks and, in 855, challenged the huge army of King Louis the Pious at Devin and, in 857, even conquered Duke Carloman and established, in 857, a peace treaty with him.

Ratislav I wisely understood the importance of Christianizing of the Slavs and asked the Pope in Rome, in 861, to send a Bishop to his kingdom. His request fell on deaf ears in Rome and, so, in 862, he asked the Byzantine Emperor Michael III to send him a Bishop and religion teachers. The famous letter from Ratislav I to Emperor Michael III began with these words: " ...We, the Slavs, a simple people, have no-one to teach us the truth..." The Emperor agreed to his request and sent Ratislav I, two apostles, Cyril and Methodius, who were brothers and natives of the city of Salonika (today Thessalonika).

They, even before leaving the Byzantine Empire, had created the first Slavic alphabet, called Glagolitic and had translated several religious works into the Slavon language (ancient Slav).

After their arrival in the principality of Rastislav I, Cyril and Methodius, accompanied by a large group of scholars, founded, using as a model the Academy of Constantinople, the first academy in Slovakia and further developed writing in the Slav language, to which were translated other religious texts and in which several literary works, poems and judicial acts were written (Proglas Poem, the work " Warnings to Lords, a judicial Code for the common people, ", etc...)

The work of Cyril and Methodius includes:
-First Slav alphabet
-First translations into the Slav language -- the Slavon (ancient Slav) in 862
-First large Slav school (863)
-First translations and first literary, philosophical and legal works in the language of the    Subdanubian Slavs -- Slavon (863-886)
-Establishment of the Slavon language as the liturgical language (867), first liturgical Slav language after Hebrew, Latin and Greek
-First Slav Bishop - Cyril (Constantine) (868)
-First legate of the Holy See for the Slav countries - Methodius (869)
-First archdiocese in the Slav countries - Bishop Methodius (869)
-The first archdiocese was not established in Prague until 1344.
From 869-871, the intrigues and military attacks led by the Eastern Franks against the principality of the Slavs intensified. After Rastislav I was taken prisoner by the Franks and lost his sight, and after the large anti-Germanic insurrection of Slavomír, Svätopluk acceded to the throne of the principality.
From 872-876, Svätopluk conquered the armies of Louis several times and kept his independence.
In 880, Pope John VIII, by the act  " Industriae tuae " crowned Svätopluk King and gave his kingdom the protection of the Holy See.

Important events during the period of the Kingdom of Svätopluk:
- 874 Occupation of the Vistule Basin by Svätopluk
- 882 Occupation of the territory of Bohemia/present day Czech Republic excluding; Moravia
- 883 Invasion and Occupation of Pannonia
- 889 Occupation of the territory of Lusatian Serbs
- 890 Treaty with Arnoul, confirmation of the sovereignty of Svätopluk I in Bohemia
- 892 Driving back of the common attack by the Frank, Alaman and Bavarian armies and the Magyar tribes
- 893 Driving back of the attack by the armies of Arnoul, and upon his request, the signing of a peace treaty with Svätopluk
- 894 Death of King Svätopluk I, peace for the Slavs with the Bavarians, first invasion by the Magyars into the Transdanubian region.

The death of King Svätopluk brought about the progressive disintegration of the largest Central European empire and eventually disappearance due to the incessant invasions of the allied Bavarian armies and the Magyars. However, the first act, which led to the disintegration of the Empire, was caused by the Slav Dukes of Bohemia (present-day Czech Republic) in 895, which detached itself from the Empire of Svätopluk and asked Emperor Arnoul of Ratisbonne for his protection against the Slavs.

In 897, Mojmír II tried once again to conquer the territory of Bohemia, but failed, and in 898, a struggle for the throne broke out between King Mojmír II and his brother, Svätopluk II. Mojmír II fought off the attack by the Bavarian armies, who had been joined also by military troops of the small Czech Lords and he had Svätopluk II imprisoned.

In 902 and at the beginning of 906, Mojmír II twice pushed back attacks from the Magyar armies, which resulted in their fleeing. However, during their next raid in the South, Mojmír II as well as Svätopluk II were killed and the Magyars pillaged the Southern regions of Slovakia. This was the beginning of the progressive disappearance of the independent Slav State and chronicles of that period describing the battle of the Bavarians against the Magyars on July 4, 907 make no mention of any participation by Slav armies.