situations of conflict between state and national law, national law prevails due to?

Federal law always supersedes state laws due to the Supremacy Clause which is found in Article IV of the US Constitution. Federal Laws apply to all 50 states whereas State Laws apply only to the individual states. Some laws are applicable at the state level such as the crime of murder (as long as it did not occur on Federal property). State laws differ regarding the prosecution and sentencing for murder. The Federal government does not interfere with State jurisdiction with this crime but the are some violations that are Federal that may conflict with state laws. Immigration is an example in which some states may "legalize" groups of people while the Federal government does not. In this case, the Federal laws supersede the state laws and Federal immigration laws are imposed.