Here's a short story:

Kievan Rus' begins with the rule (882–912) of Prince Oleg, who extended his control from Novgorod south along the Dnieper river valley in order to protect trade from Khazar incursions from the east and moved his capital to the more strategic Kiev. Sviatoslav I (died 972) achieved the first major expansion of Kievan Rus' territorial control, fighting a war of conquest against the Khazar Empire. Vladimir the Great (980–1015) introduced Christianity with his own baptism and, by decree, that of all the inhabitants of Kiev and beyond. Kievan Rus' reached its greatest extent under Yaroslav I (1019–1054); his sons assembled and issued its first written legal code, the Rus' Justice, shortly after his death. 

The term "Kievan Rus'" (Ки́евская Русь Kievskaya Rus’) was coined in the 19th century in Russian historiography to refer to the period when the centre was in Kiev. In English, the term was introduced in the early 20th century, when it was found in the 1913 English translation of Vasily Klyuchevsky's A History of Russia, to distinguish the early polity from successor states, which were also named Rus. Later, the Russian term was rendered into Belarusian and Ukrainian as Кіеўская Русь Kijeŭskaja Rus’ and Ки́ївська Русь Kyivs'ka Rus’, respectively. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: When did Kievan Rus' began?
Guess: 882

Question: by whom?
Guess: unknown

Question: When did they change their religion?
Guess: Sometime between 980–1015

Question: who was the leader?
Guess: Vladimir the Great

Question: how did he do it?
Guess: with his own baptism

Question: What was Prince Oleg trying to protect?
Guess: trade

Question: When did the name start being used?
Guess: 19th century

Question: why?
Guess: to refer to the period when the centre was in Kiev

Question: Why was it moved there
Guess: unknown

Question: how did they have their first major expansion
Guess: war

Question: What was issued?
Guess: legal code

Question: by whom?
Guess: Yaroslav I's sons

Question: what else was he known for?
Guess: Kievan Rus' reaching its greatest extent

Now answer the following question in the same format.

Question: who did they fight against?

unknown