Explanation:

- The passage discusses a situation where there are two competing sides, and the outcome is uncertain.

- The correct word should fit into the context of determining which side will ultimately prove superior or triumphant.

- Option 1: "successful" - could fit in terms of achieving success, but does not directly imply winning in a competitive context.

- Option 2: "thriving" - suggests flourishing or doing well, but not necessarily winning over another side.

- Option 3: "victorious" - this word directly implies winning or conquering, fitting the context of determining which side will succeed in a contest.

- Option 4: "failing" - suggests losing or not succeeding, which contrasts the idea of either side proving superior.