This topic should be marked as satire.
France, UK, Germany and Spain as well as Portugal conquered the world.
What have the slavs cpnquered? The empty taiga. Spartans? Never more than their city state.
All slav countries combined have a smaller GDP than Italy.
You say we French and British ect employed foreign soldiers? Y we did so in our colonies. Russia never could follow that policiy. Russia never left the continent of its origin.
You say tribes like huns, slavs and spartans were sucessful in history and Brits, French, Germans ect are not?
Time for reality check?
Spartans never went beyond their home region. They later on got crushed, romanized and assimilated in the general greek population. Greece later on was 500 years udner ottoman rule and today is a puppet state in the EU
and gets dictated what to do from Germany, France and banks.
The huns? Got crushed and pushed back where they came from. Today Mongolia is a poor 3rd world country and an absolute vasall of China
Majority of mongolians has no acess to electricity, running water and clean toilets.
The slavs? Are an economic dwarf that have conquered the taiga. Had zero influence on global history and still suffer from poverty and systematic corruption.
Meanwhile nations like the UK, France, Spain, Germany shaped the world as we know it. Brought our culture even to remotes jungle. Forged nations like USA, Canada, Brazil, Argentina.
So with all due respect, if you see sucess to exist in poverty stricken 3rd world countries without any global influence...
I would not even want hang dead over a fence in Mongolia.
My guess is we have very different definitions about sucess.
If i go by your standards the australian aboriginies are the most powerful empire on this planet. They have been sucesfsul for 40.000 years! So they are even more powerful than your "slavic empire"