Who won World War 1 and why?
WW1 was won by the Allied Powers, which consisted primarily of
Great Britain, France, the United States. The Russian Empire is not
considered to have won, as though it was an initial member of the
Allied side (a founding member of the Triple Entente with the U.K.
and France), it sued for peace in 1917, and suffered from internal
revolution shortly thereafter.
As to why, that is far to complex an answer for here. Spell
check your answer