Tribe's self-defence system incomplete — what a shame! (5)
I believe the answer is:
judah
'tribe's' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for judah that I've seen before include "A son of Jacob and Leah" , "Jewish tribe,kingdom" , "The most powerful of the twelve tribes of Israel" , "Tribe" , "One of 12 tribes of Israel" .)