Is war government sanctioned murder?

Short answer - no.

No, not as defined by any country's laws or by any dictionary. By the way, you're missing a hyphen. It makes your question hard to read. Your question should read: "Is war government-sanctioned murder?" When you use the participle of a verb as an adjective and include a subject with the participle, a hyphen is required (e.g., dandruff-covered coat, light-filled room, ballad-singing diva).