I see you now agree that there was a large military and naval force ordered to enter Charleston Harbor. This was an act of war unapproved by the government.
His speech revealed his vicious intent.
I assume you mean to say Congress.
But of course Congressional approval is not required for the President to move troops between US facilities.
For it to be an act of war it would have required the president to agree that SC had actually seceded and was now (part of) another country.
Which of course neither Buchanan nor Lincoln ever conceded.
Your argument that it was an act of war is therefore a classic example of a well-known logical fallacy.
http://en.wikipedia.org/wiki/Begging_the_question