The most common and most likely answer to this crossword clue is the 6 letter word SPOILS
I've seen this crossword clue in The Guardian
S
P
O
I
L
S
Buddy explains!
The straight part
We know that "Valuables taken in war/Valuables taken in war/Mars/Mars" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case valuables taken in war/valuables taken in war/mars/mars = spoils.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 SPOILS mean?
SPOILS verb- To strip (someone who has been killed or defeated) of their arms or armour.
- To strip or deprive (someone) of their possessions; to rob, despoil.
- To plunder, pillage (a city, country etc.).
- To carry off (goods) by force; to steal.
- To ruin; to damage (something) in some way making it unfit for use.
- To ruin the character of, by overindulgence; to coddle or pamper to excess.
- Of food, to become bad, sour or rancid; to decay.
- To render (a ballot paper) invalid by deliberately defacing it.
- To reveal the ending or major events of (a story etc.); to ruin (a surprise) by exposing it ahead of time.
- That which is taken from another by violence; especially, the plunder taken from an enemy; pillage; booty.
- Public offices and their benefits regarded as the peculiar property of a successful party or faction, to be bestowed for its own advantage.