not necessary. A modern conflict can happen in the disputed area without anybody bombing cities of the opponent. iPhones will continue to be shipped to US from China while J-20 will be playing hide-and-seek with F-22/35 over, say, the South China Sea. A very related example - Great Britain didn't bomb Buenos Aires 32 years ago nor did Argentina strike at anything Britain's outside of the war zone.
Argentina didn't have the military capability to attack anything outside of the war zone. Great Britain simply exercised restraint in their attacks on the mainland.
that is the main point. Any country escalating a conflict outside the war zone would pay a heavy price that would make it not worth it. They wouldn't win the war that way, they'd lose it. It is not their good will, it is just their desire to win, not lose. Bombing Argentina outside of war zone would pit Great Britain against whole world - a loosing position, or not-wining at the very least. You wanna fight - take it outside and everybody is happy.
