Short answers, pulled from the story.
Procopius described early Slavs as barbarians living under democracy who worshipped Perun, the maker of lightning. These people dwelt between the upper Vistula and Dnieper rivers east of Germanic tribes and west of Iranian Sarmatians.
Frankish merchant Samo supported Slavs against Avar rulers and became ruler of the first known Slav state known as Samo's Empire during the 7th century. This polity likely did not outlive its founder but laid foundations for later West Slavic states.
Standardized Slavic languages include Belarusian Bosnian Bulgarian Croatian Czech Macedonian Montenegrin Polish Russian Serbian Slovak Slovene Ukrainian. Cyrillic alphabet serves Orthodox Christians while Latin script is used by Catholics and Muslims like Bosniaks who also employ both alphabets in Serbia.
By 1878 only three majority Slavic states existed globally: Russian Empire, Principality of Serbia, and Principality of Montenegro. Bulgaria remained effectively independent but de jure vassal to Ottoman Empire until official independence declared on the 3rd of March 1908.
Nazi Germany planned Generalplan Ost starting in early 1941 to exterminate millions of Slavs in Eastern Europe over twenty-five to thirty years. Hitler intended to eliminate most West and East Slavs from their native lands to create living space for German settlers.