Explain the doctrine of federal preemption

What will be an ideal response?

The Supremacy Clause of the U.S. Constitution is the basis for the doctrine of federal preemption, a constitutional doctrine stating that in an area in which federal regulation is pervasive, state legislation cannot stand. This doctrine is used to strike down a state law that, although it does not directly conflict with a federal law, attempts to regulate an area in which federal legislation is so pervasive that it is evident that the U.S. Congress wanted only federal regulation in that general area. It is often said that in these cases that federal law "preempts the field." Cases of federal preemption are especially likely to arise in matters pertaining to interstate commerce, such as when a local regulation imposes a substantial burden on the flow of interstate commerce through a particular state.