What is one reason that the constitutional convention decided they needed a document to replace the?

Because the articles did not include details about a unifying leader and also the articles lacked an outline for a tax system that would pay debts.

Ongoing civil wars western roman empire finally collapsed476 c.e. romulus, the last of theroman  emperors in  the west, was overthrown by the germanic leader odoacer, who became the first barbarian to rule in rome. the order that the  roman empire  had brought towestern  europe for 1000 years was no more.