According to the United States Constitution, certain powers are denied to the national government, such as the taxation of exports. The federal government also cannot interfere with an individual state's ability to carry out its responsibilities.
The Constitution also denies certain powers to state governments. For example, a state cannot make a treaty with any foreign government. States are also prohibited from making money, granting titles of nobility, or making any laws that impair the obligation of contracts. In order for a state to make agreements or to collect duties on imports and exports with other states, congressional permission is required.