Are fortifications and defenses the ONLY thing needed to defend a Kingdom/Country?

Explanation:

Natural fortifications also helps defend a country. For example the Alps in Italy defends them very well. Rivers can also be a defensive position a country can fall back to. So no, fortifications and defenses arent the only thing. Nature is able to help too.

the us constitution is a living document, meaning that it can be changed over time as the country changes.

congress also has implied powers, which derive from the necessary and proper clause of the constitution and permit congress "to make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states.