During and after the American Revolution, America's greatest leaders and thinkers feared nothing more than a centralized government which had too much control over its citizens. To avoid creating such a government, they drafted the Articles of Confederation, a document that gave almost all power, short of international affairs, to the American State Governments. The main issues with the Articles of Confederation were that it would not have held in a time of military crisis, required too much of a majority to pass legislation, and provided no effective means of national fund-raising. From 1781 to 1789, the Articles of Confederation did not provide the United States with an effective Government.
The Articles of Confederation gave too little power to the centralized government to act in times of military crisis. The United States at this point still had a tiny standing army, and the Federal Government had no means to draft and equip one. This left it up to the states to provide their own militia and weapons (which they could not have in peace time). Under this system, a state could mobilize only once attack was imminent. Shays" Rebellion is a perfect example of how the system fails. Massachusetts had to use private funding to raise a militia to put down Captain Shays and his fellow insurgents. Congress only provided 1500 troops and the troops got to Massachusetts after much of the fighting had already taken place. If there were a surprise attack from another nation, or even worse an armed conflict between two states, Congressional action would be tedious at best and useless at worst.
A second problem with the Articles of Confederation was that 9 out of 13 states had to agree to get anything done. Not only is this greater percentage-wise than the amount needed under the Constitution, but it also meant that if a law or bill hurt more than four states, it would never be able to pass.