A declarative statement ends with a period.
An interrogative one ends with a question mark.
An exclamation ends with an exclamation point.*
Makes one wonder why our country was born with a "Declaration of Independence," when it seems like an exclamation might have been more appropriate.**
(Seems like something that they might have wanted to get more excited about.)
Could have been worse, though.
At least we didn't start our country with an interrogation of independence.
e.g. "Independence, where were you on the evening of July 4, 1776?"
* They got a little lazy on this name, it seems.
Perhaps coming up with the other two was exhausting.
** The Exclamation of Independence would have started out, "Wheeeeee!, the people..."