Question

why was the articles of confederation so weak

Answer 1

They gave very little power to the central government and if the central government wanted to pass something all the states would have to ratify it.

Answer 2

Keeli_Grace is right. Under the Articles, each state could technically make separate trade agreements and decide whether or not to give money to the central government. Each state was like a mini-nation in terms of foreign trade and taxation which really damaged the new government's ability to fund the army and remain solvent. It's like being in a meeting with everyone having their own ideas and a weak leader who tries to pick the best one with no one listening.