In the Constitution, there are some powers that are granted only to the federal government. These powers are called the enumerated powers. There are some powers that are granted only to the state governments. These are called the reserved powers. There are also some powers that both the state governments and the federal government share. These are called the concurrent powers.
The enumerated powers given to the federal government are ones that are off limits to the state government. For example, only the federal government can make treaties affecting the entire country. When a war ends, only the federal government negotiates the peace treaty. Only the federal government can make or print money. Unlike during the days when the Articles of Confederation was our plan of government, states are not allowed to make or print money. The federal government can only do this. The federal government also controls interstate trade and foreign trade. Another enumerated power is that only the federal government can declare war. States aren’t allowed to go to war. Finally, only the federal government can create a post office.
It should also be noted that states are not allowed to pass laws that go against federal laws. The Constitution is the supreme law of the land. Federal laws always have priority over state laws. States aren’t allowed to nullify federal laws. There are several things the states may not do under the plan of government created by the Constitution.