Great Moravia (Latin Moravia Magna) was a Slav state existing on the territory of present-day Moravia and Slovakia between 833 and the early 10th century. The first use of the designation "Great Moravia" stems from Constantine VII Porphyrogenitos in his work De Administrando Imperio (around 950 A.D.). "Moravia" did not refer (only) to present-day Moravia, but either to the country to both sides of all the Morava river, or probably to a state whose (today unknown) capital was called Morava. "Great" refers to Moravia plus the annexed territories.
A kind of predecessor of Great Moravia was the Empire of King Samo in around 623-658 in Moravia, Slovakia, Lower Austria (probably also Bohemia, Sorbia at the Elbe, and temporarily in Carinthia), which probably has not been a true state, but only a tribal union.
In the late 8th century, the Moravian basin, situated at an important north-south trade route, began to flourish. Two important states (principalities) emerged in this territory: the Moravian principality largely in present-day Moravia (led by prince Mojmír I, probable center: Mikulčice) and the Nitrian Principality (Principality of Nitra) in present-day western, central and northern eastern Slovakia (led by prince Pribina, center: Nitra).
What the historians and Porfyrogenet design as "Great" Moravia arose in 833 by Mojmír\'s conquest of the Nitrian Principality. The empire came under the rule of the Princes Mojmír I (833-846), Rastislav (846-870), Svatopluk (871-894) and Mojmír II (894-?) who built a great empire. Rastislav asked the Byzantine Emperor to send people who could interpret the teaching of Christ in the Slavic vernacular. Two of the people sent, Cyril and Methodius, laid the foundation of the Slavonic script, and thus of Slavonic literature (see e.g. Glagolitic alphabet).
The territory of Great Moravia was as follows:
The state has been a state of present-day Moravians and Slovaks. The western part of Great Moravia's core (=present-day Moravia) was finally conquered by Bohemia in early 11th century and its population was czechicized in the 19th century. The eastern part of the core (=present-day Slovakia) was finally conquered by the Magyars (Hungarians) in the 11th-14th century and its population developed into present-day Slovaks in the 10th century. Great Moravia is often considered a predecessor of Slovakia.
The inhabitants of the core of the state were designed as "Slovieni" (which is an old Slavic word basically meaning "Slavs" and was also used by (future) Slovenians and Slavonians at that time) or "Moravian peoples" by Slavic texts, and as "Sclavi" (i.e. Slavs), "Winidi" (i.e. Slavs), "Moravian Slavs" or "Moravians" by Latin texts. The present-day terms "Slovaks" / "Slovakia" (in Slovak: Slováci / Slovensko) and "Slovenes" / "Slovenia" (in Slovene: Slovenci / Slovenija ) arose later from the above "Slovieni".
As for the history of Bohemia - annexed by Great Moravia 888/890-895—the important year is 895, when the Bohemians broke away from the empire and became Frankish vassals (vassals of Arnulf of Carinthia) and gradually an independent Bohemia, ruled by descendants of Premysl, began to emerge.