The correct answer is Option c - Roman Christianity led to more military conflicts.
While Roman Christianity may have had impacts on the empire's expansion later in its history, it actually played a minor role in the early and rapid expansion phases. In fact, during these periods, Roman rulers often tolerated and even adopted local religious practices to appease conquered populations and facilitate integration. Therefore, while Christianity may have influenced later conflicts, it wasn't a significant factor in the initial economic drivers of Rome's expansion.
The other options all directly contributed to Rome's military strength and ability to conquer new territories:
a - Arming soldiers : Well-equipped and trained legions were crucial for Roman victories.
b - Providing for soldiers : Ensuring soldiers were well-fed and cared for helped maintain morale and combat effectiveness.
Thus, Oc is the only option that doesn't align with the economic reasons behind Rome's early expansion.