Was the Revolution a sin? War is certainly a consequence of sin. But a sin? I think it's very hard to say in our position. In war, each side always believes "God is on our side", so they believe their actions are always with reason and condoned by Almighty. In reality, the only wars we know that God authorized were the ones in the OT that God clearly ordered.
I think the Declaration of Independence, in the first few sentences, quite clearly explains it all.
1) We believe God gave us certain rights.
2) We believe man establishes government to secure those rights.
3) We believe the current government is not securing those rights.
4) We believe a new government will secure those rights.
War is a reality that will never go away while man is imperfect. And even though war with one nation against another is a horrible thing, I think, sometimes, it is necessary. I even believe acts of rebellion against established order is necessary (independence, secession, civil wars, whatever you want to call it). In fact, I think it's healthy for the People to overthrow their government often, so they can secure their freedoms and rights.