We did give them a demonstration, and unfortunately innocents did die. That demonstration was Hiroshima.
Unfortunately, the Japanese govt, for whatever reason, didn't think, even with that demonstration, that nukes were capable of extreme destruction. Or if they did, they chose to ignore. That's a classic example of a distinction without a difference.
The result? Nagasaki.
So if dropping a nuke on Hiroshima didn't convince them of the power of nuclear weapons, what in the blessed name of Elvis makes you think setting one off on a military outpost would have better results?