Which of the following powers belongs to the states?

Regulating intra-state trade is a power that clearly belongs to the states as outlined in the U.S. Constitution. This authority allows states to manage commerce and economic transactions occurring within their own borders, fostering local economies and addressing specific regional needs without direct interference from the federal government. This power is rooted in the understanding that states have the best insight into the practices and requirements of businesses operating solely within their limits, which contributes to both state economic growth and the welfare of local residents.

In contrast, declaring war, printing money, and making treaties are powers expressly reserved for the federal government. These powers are critical to national security, maintaining a stable economy, and managing foreign relations, respectively. They require a unified approach that is essential for maintaining order and consistency in matters that affect the entire nation. Thus, the correct focus on intra-state trade underscores the role of states in governing their specific economic landscapes while recognizing the separate, broader powers held by the federal government.