The states entered into a union for the purpose of protection against foreign invasions and Section IV of Article IV ensured that the government know that it was their department. The only part of Article IV I found surprising was Section III with the addition of the new states, I didn't know Congress had the power to accept new states and that interested me. I found Article IV to be a general overview of the states in which the founders tried not to limit the actions of the states but nevertheless ensure peace among them.