The sin of the Twelve Spies had more negative ramifications than any other sin in the entire Torah.  It wiped out the entire generation.  It prolonged the building of the Beis Hamikdash for hundreds of years.  It gave birth to what is now called Tisha B’Av; the saddest day of the Jewish year.  The question is what was so bad about what the Twelve Tribes did?  How do their actions explain the amount of pain and bloodshed that they brought about?  The answer might surprise you.