Why does the power to declare war belong only to the national government?

well let's see i know a little about the fall of the roman empore but what to say i do not have a clue of what to say. (that's 28 words) i learned about it in social studies it was quite boring really my teacher talks a lot, like a lot then gives us a bunch of work sheets not too many though.( that's 60 words)i actually almost fell asleep in class of course i really like that teacher of course she is really nice. i actually don't remember much from that class i got a b without any notes (it was an open notes test)(that's 95 words) i'm wasting time but i've gone too far to stop now i'm sorry i haven't said really any thing on the topic at all sorry not sorry haha jk.(that's 125 words ) (mike drop)