Under the United States Constitution, the federal government has the power to "provide for the common defense" and "insure domestic tranquility." This includes the power to raise and support armies, as well as to regulate the militia. As such, the federal government has the authority to require the states to provide assistance in the form of money or troops for the purpose of national defense or domestic tranquility.
However, the Constitution also provides for a system of federalism, in which the states retain certain powers and responsibilities. This means that the states are not simply subject to the will of the national government, but rather are sovereign entities that must be treated with respect and consideration. As a result, the federal government may not unilaterally demand assistance from the states without due consideration of their interests and concerns.
In practice, the federal government often works cooperatively with the states to address national defense and domestic tranquility concerns. This may involve providing funding or other resources to the states, as well as seeking their input and cooperation in decision-making.