Can u tell me the book's name

[jackprince]

It was book about a woman Sergeant in Marine. She was sent to a diplomatic mission under a young Lieutenant, which turns out to be a gruesome battle.

It's world is something like consists of elder races who abhors violence so recruited human and two other race to fight their battle.

Can you tell me the name of the book??

[Mostlyharmless]

This could be "Valor's Choice" by Tanya Huff. Best to buy it as half of "A Confederation of Valor".

[Jim diGriz]

This could be Alan Dean Foster's "A Call to Arms". The scenario fits and there is a woman soldier in the book although she is not the central character.

Having dug out my old copy of 'Valor's Choice' I'm more inclined to believe Mostlyharmless is correct, it has been a while since I read it.