War was not the only inevitable means to decide that dispute.

Answer: Option C

Indefinite : lasting for an unknown or unstated length of time.
Imminent : about to happen.
Unavoidable : not able to be avoided, prevented, or ignored; inevitable.
Improbable : not likely to be true or to happen.
Inevitable : certain to happen; unavoidable.

Synonym of Inevitable is Unavoidable