In fact you know nothing about origin of Slavs.
Thats why they are not in this mod.
But its not your fault , its fault of current education system and manipulating history.
Some greek guy , philosopher or historian or wtf talking about Slavs around 490 B.C
In my country there are few archeological places with drawings of Perun (Slavic god) on huge rock what was dated cca 3000 years old and goverment and official scientists ignoring it.
There are scripts showing that language of Vandals are 87% same as today eastern Slovakian accent.
So Vandals was germans right? llol.
As i said : its not your fault ^^ , you are just being brainwashed 24/7 and Slavic history is most manipulated thing on earth so who can wonder why you dont know the truth