Which political systems would have a "supreme leader"?

Historians are concerned with the accuracy of their writings and readings but are also aware of the inability of authors to know every angle of every story biases, perspectives, beliefs, and a variety of other differences history being told by one person at a time no one being totally accurate, as hard as we try really need on this, and you^^

What is significant about official languages in russian republics? why would it matter?

What are some effects outside of europe because of world war 1?