Why did the leaders of the united states decide to create a new plan of government in 1787

The Articles of Confederation was enacted in 1781, the time when the whole country was under the loose confederation of states, where all states working like autonomous countries.

The federal government was composed of a single legislature, The Congress there was neither a president nor judicial branch. The central government, under the Articles, was proved to be too weak to impose their rules and regulations and therefore had no authority. Due to these issues, delegates created a new plan in  1787 convention, for a powerful federal government with three branches i.e executive, legislative and judicial followed by the system of checks and balances to assure that no single branch could exercise too much authority.

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may i ask what challenges?