The most accurate response is: As the Romans conquered territory, they gained access to trade resources, which encouraged more expansion.
This statement captures the essence of how Roman expansion was closely tied to trade dynamics. As the Romans expanded their empire, they sought out new territories that offered valuable resources, better trade routes, and access to lucrative markets. Control of these trade routes and resources was a significant driver for Roman military campaigns and expansionist policies.
Other options present some elements of truth but lack the comprehensive connection between expansion and trade illustrated in the chosen response. For instance, while the idea of punishment for not trading is an interesting angle, it oversimplifies the complex motivations behind Roman expansion. The claim that there was no correlation also ignores the significant impact that trade had on the growth of the Roman Empire. Lastly, while protection of trade interests was a concern, the primary motivation often intertwined with gaining resources as a direct result of expansion.