To add to Keb’s post about royal titles, in historic Russia, there were many different competing principalities of which the rulers were called princes, not kings. There was no real supreme power until the emergence of the Grand Principality of Muscovy (Moscow) under Ivan the Terrible, who was the first to be crowned in 1547 as the czar (which is the Russian equivalent of the Latin title “caesar”).
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"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy