Basically, It was the birth of the nation because it was saying; We don't want to be associated with the British any longer. We are separating from them, and declaring ourselves the United States of America.
The declaration of independence the birth of the nation because America was finally free from Britain. America didn't have to take order from Britain and got to make their own rules (the ones of the declaration of independence). This declaration justified the colonies and the purpose and foundation of government and by explaining how the British government had consistently failed to meet the standards of those truths.
