What makes federalism unique is that the distribution of power between state and national government is such that it is not clear who has the final authority. In practice, the tendency in most countries has been for the federal government to have the greater share of power.
According to PBS, in a federal system, the states have a level of autonomy and independence because these existed prior to the national government and granted that national government its authority. The U.S. Constitution outlines the responsibilities of the different branches of the federal government and then declares that all powers not expressly given to it are reserved to the people and the states. Thus, authority over issues like war and foreign relations ultimately rests with the federal government, while authority over penal law lies with the states. As time has passed, however, the federal government has exerted greater influence in affairs previously considered the exclusive domain of the states.