Are you that thick?
If a foreign country supports cyber attacks against US government computers which do the work of the US government, that amounts to declaring war on the US government because you are disrupting the proper functioning of the US government. If a foreign power/country disrupts a country's normal functioning by attacking that country's assets (which includes computers doing govt work), that amounts to declaration of war - by international diplomatic norms.
Now did you understand that part? If you have a small business and someone else wants to create disturbance by, not physically destroying your business premises, but by stopping electrical supply or water supply, that would still be considered an attack, right? How would you stop attacks on your business? Countries are no different.
Comprende?