War between Israel and Iran (with or without US involvement) will be catastrophic for the world. People will die, more people will be motivated to join terrorist groups unleashing even more violence, and the world will be thrown into a terrible economic crisis from the rise in oil prices. Everyone in the world will suffer as a result.
Moreover, military analysts in Israel and the US say it would at best only delay, not destroy, Iran's nuclear capability. In other words, war will not solve this problem; it'll only lead to destruction and suffering.