Gary J. Schmitt and Joseph M. Bessette at AEI:
The practice of executive power from the early days of the Revolution to the Constitutional Convention was complicated by the division of governance between the central authority – first the Continental Congress and then the Congress under the Articles of Confederation – and the thirteen newly-independent states. Thus, the executive power was divided between the two: Congress assumed the authority over foreign and defense matters, while state governors were largely tied, at least formally (and in the absence of delegations of extraordinary authority), to administrating measures enacted by their legislatures. Hence, the various lessons learned about the practice of executive power from this decade-plus of self-government were themselves complex.
At the level of the Union, the major takeaway was that executive power in the hands of a plural body—be it the Congress as a whole or one of its committees—was functionally inept when it came to dealing with the demands of the war and the diplomacy necessary to secure American independence. Nor was Congress adept at day-to-day administrative tasks. Too many hands on the tiller caused delays and the blurring of responsibility for decision-making. Gradually, members came to understand that giving charge of foreign, defense, and fiscal matters to single individuals promoted coherent and effective management. If the government was to possess the qualities of dispatch, decisiveness, and secrecy—let alone administrative efficiency—the executive authority would not only have to be unified but also enjoy some level of institutional independence from the legislature.
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In fine, the practice of republican rule in the decade following the Declaration of Independence had produced a new sense among many Americans on the need for, the advantages of, a firm and energetic executive power. That change had taken place at both the state and the national level, with different emphases arising from different circumstances and distinct governing tasks. Once the decision was made to jettison the Articles of Confederation, the challenge was how to incorporate in a coherent way the various lessons learned since independence so as to create an effective and safe executive in the new national, but still republican, government. Separation of powers provided a popularly accepted template for attempting to do so. But the devil would be in the details and, not surprisingly, this explains why deliberations about the executive went virtually the whole length of the Constitutional Convention.