You keep saying that in the face of reality. A nation is quite clearly free to annex land from which attacks are being launched incessantly for use as a buffer zone. Let's put it in terms you might actually understand:
A new government rises to power in Mexico, led by an insane nationalist who has never gotten over the "theft" of Texas from Mexico and resents the affluence of the Texan towns he can see just over the border, blaming America for poverty in Mexico.
You live in a Texas town on the border with Mexico. Suddenly, one night, explosions rock the town, buildings are blown to pieces, people are shredded in the streets, gangs of Mexican nationalists roam the streets, attacking anyone who looks like an American. You watch your wife and children murdered before you, yet you manage to escape. With me so far?
The US, naturally outraged at this development, sends the army to the border and notifies everyone within a mile of it on the Mexican side to leave or be killed by what's coming. After the appointed time, they level everything in that zone, then declare it a DMZ, complete with patrols, drone flights and barbed wire fences.
What is your response? "Okay, that's too much. We killed innocent people, we committed war crimes, we should have had restraint, it wasn't fair because they don't have the weapons we have, we have to give the land back"?