Which of the following powers is specifically related to state governments?

The power to regulate trade within the state is specifically related to state governments because it falls under the purview of state sovereignty and responsibility for local commerce. Each state has the authority to create and enforce laws that govern trade practices, including business regulations, taxation on local businesses, and the enforcement of contracts, which are essential for maintaining economic stability and growth within that state.

Other options, while important governmental responsibilities, are not specific to state governments. Conducting foreign relations and declaring war are powers reserved for the federal government, as these actions have implications that extend beyond state boundaries and require a unified national approach. Establishing post offices is also a power designated to the federal government to ensure mail delivery is consistent and standardized across the entire country. Thus, the power to regulate trade within a state is a key responsibility of state governments, focusing on their role in managing internal economic activity.