americas' eavesdropping technology

It is apparent from many of the posts that the US eavesdropping technology is at a high and sophisticated level.However,how is all this information to be used?Is it right to wage war against a country because you have overheard conversations that make you believe that the persons/country are planning to attack you in one form or another.How much credibility can you put on this information?Can you kill on this information?Will this type of surveillance be applied on all countries and the information gathered used to threaten governments with pre.emptive action?
It may be Australia at some time in the future under a labor government or a green government.
"I shot the dog as I believed it wished to bite me...."