We may not be sure today that an invasion would have been necessary, but they certainly weren't sure or unanimous about it back then. The important thing is the bomb was the surest way to end the war at the time. The bottom line is that the war ended within days of the decision, with a loss of life no greater, if not less than any other conceivable military alternative. The best case for the bomb was given by Alex Roland of Duke University, who in Technology Review observes that since the bomb topped the peak of worldwide war deaths, we've lived in the safest half-century since the 1800's. Today it's less than one percent and falling, and it's unlikely that my toddler sons will ever be called to serve in uniform.
World peace is almost a reality today, thanks to the specter of nuclear warfare.
Japan and Germany together never had the global reach or destructive power of what America has today. But I, for one am thankful that we fear no evil in the valley of darkness because we are the toughest SOB's in the valley. Yes, we should mourn and remember those who died at the hands of an untested new technology, but it is more important that we remember the passing of an age when war deaths measured 50 million, not just the couple of hundred thousand at Hiroshima or Nagasaki at the hands of the Americans.