The most common and most likely answer to this crossword clue is the 6 letter word MONGOL
I've seen this crossword clue in The Daily Telegraph
M
O
N
G
O
L
More clues leading to the result MONGOL
Buddy explains!
The straight part
We know that "Principally member of nation Genghis originally led" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case principally member of nation genghis originally led = mongol.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MONGOL mean?
MONGOL noun- A person from Mongolia; a Mongolian.
- A member of any of the various Mongol ethnic groups living in The Mongolian People's Republic, the (former) USSR, Tibet and Nepal.
- (usually mongol) A person with Down's syndrome.
- A member of the nomadic people from the steppes of central Asia who invaded Europe in the 13th Century.
- A member of the Mongols Motorcycle Club of California, United States.