Answer: The Articles of Confederation
Detail about the Articles of Confederation (which were ratified in 1781):
The Articles of Confederation concentrated power in Congress, the legislative branch of government. There would be a President as an executive officer, but he was chosen from a Committee of the States that was appointed by Congress. The American colonists, in forming the new nation, initially showed much concern about limiting any executive branch power, fearing it would become like the king of Britain had been in wielding excessive power.