It becomes illegal when they built settlements and transferred populations, which they did between 1967 and 1981. In some bizarre alternate universe, I'm sure Israel didn't do those things. But they did in this one. Then they annexed it, also illegal.
If I am allowed to park someplace between 4 PM and 6 PM, but I park there at 7 PM, would you say I was parking illegally? Of course. My description isn't even wrong, although I'll gladly say it was if it means you guys will actually address the overarching point of my post. But I doubt it. You'll just get slapped down again.