Third Planet by Murray Leinster

The "Lotus" went on toward Planet Five, leaving a world which should have been alive and wasn't, to go to a world which should not exist, but did. On the way there was argument which became embittered. In theory, the discoveries made by a Survey ship became automatically available to all the world. But the discovery of Three in the state it was in would have political results on Earth.

It was -- and is -- a fact that nobody really believes in death until he sees a dead man. And nobody can believe in the destruction of a planet unless he's seen the corpse or color photographs of it. But that was precisely what the "Lotus" had to carry back to Earth. The WDA nations would see those pictures and read the facts. They would believe in atomic war and the complete sterilization of a world. The Com nations would not see the pictures. They would continue to believe that the West -- the WDA -- was decadent and enslaved to tyrannical warmongers, and obviously could not resist the splendid armed forces of the Com association. And they wouldn't really believe there could be more than isolated, crazy resistance to their valiant troops. So they'd back their leaders with enthusiasm, and the Western peoples at most would be merely desperate.