Traditionally, warfare comprised two 'domains,' land and sea.
When aircraft entered the warfighting scenario, air was added as The Third Domain of Warfare, though 'Up, Up, and Away' did not enter into it.
Then, space became the fourth domain.
Back in June, NATO officially declared cyberspace to be The Fifth Domain. This is significant because now a major cyber attack on an alliance member can trigger Article 5 of the treaty:
The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.
Any such armed attack and all measures taken as a result thereof shall immediately be reported to the Security Council. Such measures shall be terminated when the Security Council has taken the measures necessary to restore and maintain international peace and security.
The concept was exposed by the NATO secretary-general Jens Stoltenberg to the media.
“A severe cyber-attack may be classified as a case for the alliance. Then NATO can and must react,” Stoltenberg said in an interview to the Bild newspaper. “How, that will depend on the severity of the attack,”
Stoltenberg explained that the NATO intends to respond to any assault against its members, including a cyber attack that could be considered as an act of war.
That opens the door to armed response, with conventional weapons, to cyber attacks. The idea of shoving a cruise missile up the bungholes of Bad Vlad's boys and girls as they sit in the basement of Lubyanka Square, videotaping Trump's bedroom antics, just moved up a few rungs in the options ladder.
Meanwhile, Raytheon is sponsoring a new hub for cybersecurity:
The Fifth Domain
That is to launch next week. That will be an interesting site to follow.