What were some major problems the u. s had under the articles of confederation

The central government had no real power (it went to the states). So there wasn't any way to tax people (the states had to do that), or pass laws for the whole country. The Articles couldn't be amended unless all of the states unanimously agreed to do so. What laws were put forth under the Articles were nearly impossible to enforce. The country was also deeply in debt, and without a way to tax, had no way to pay it back. Basically, the National Government was at the mercy of the states and wasn't able to get anything meaningful done (except establishing the Northwest Territory).

The answer is crop yield.