Junius Brutus Stearns, Public domain, via Wikimedia Commons
The fifty-five delegates at the Constitutional Congress had five main issues to discuss and decide.
1. REPRESENTATION
Roger Sherman, a delegate from Connecticut, proposed a legislature with two parts; states would have equal representation in the Senate, and the population of states would determine representation in the House of Representatives. This created a bicameral legislative branch, which gave equal representation to each State in the Senate, and representation based on population in the House. Small states feared they would be ignored if representation was based on population while large states believed that their larger populations deserved more of a voice. Under the bicameral system, each party would be represented in a balance of power. Each state would be equally represented in the Senate, with two delegates, while representation in the House of Representatives would be based upon population. The delegates finally agreed to this "Great Compromise," which is also known as the Connecticut Compromise.
From: https://bensguide.gpo.gov/m-constitutional-convention
2. STATE VERSUS FEDERAL POWERS
A central issue at the Convention was whether the federal government or the states would have more power. Many delegates believed that the federal government should be able to overrule state laws, but others feared that a strong federal government would oppress their citizens. The delegates compromised by allotting specific responsibilities to the federal government while delegating all other functions to the states.
3. EXECUTIVE POWERS
The framers of the Constitution had originally imagined a weak presidency and a strong legislature divided into a House of Representatives and the Senate. Under the Articles of Confederation, considerable minor paperwork had bogged down important business enough that legislators decided to establish an executive branch to deal with routine paperwork. When writing the Constitution, the framers expected the Senate to handle important issues, particularly the ratification of treaties, while the Executive would attend to matters of lesser consequence. However, as deliberations continued, the Executive branch acquired more power to deal with some of the issues that had been a source of sectional tension under the Articles of Confederation—and so the President acquired the authority to conduct foreign relations. The two-thirds clause for ratification of treaties in the Senate, as opposed to a simple majority, allowed the South a greater voice in these matters and assuaged concerns about the attempts to abandon navigation of the Mississippi.
From: https://history.state.gov/milestones/1784-1800/convention-and-ratification
4. SLAVERY
At the Constitutional Convention in 1787, delegates fiercely debated the issue of slavery. They ultimately agreed that the United States would potentially cease importation of slaves in 1808. An act of Congress passed in 1800 made it illegal for Americans to engage in the slave trade between nations, and gave U.S. authorities the right to seize slave ships which were caught transporting slaves and confiscate their cargo. Then the "Act Prohibiting the Importation of Slaves" took effect in 1808. However, a domestic or "coastwise" trade in slaves persisted between ports within the United States, as demonstrated by slave manifests and court records.
From: https://www.archives.gov/education/lessons/slave-trade.html
A compromise at the 1878 Congressional Convention agreed that the slave trade could continue until 1808. In addition, slaves would be counted as three-fifths of a person for representation in the House of Representatives; this was known as the “Three-Fifths Compromise.”
From https://bensguide.gpo.gov/m-constitutional-convention
5. COMMERCE
Under the Articles of Confederation, the individual states competed against each other economically. They issued their own currencies and even levied taxes on each other's goods when they passed over state lines.
Delegates like Washington, Madison, and Hamilton believed that promoting the free flow of commerce across state lines and nationalizing the economy would lead to America's becoming an economic powerhouse.
As Hamilton had foreseen, an "adjustment" was made, a profound adjustment that fundamentally restructured the government. A national executive was authorized and new powers were given to the Congress. These included the power to "regulate commerce with foreign nations and among the several states."
Among the proposals which were considered at the Constitutional Convention was one by Gouverneur Morris on August 20, 1787, to create a council of state "to assist the President in conducting the public affairs'" Morris recommended that the third member be a "Secretary of Commerce and Finance, whose responsibilities would include recommending " such things as may in his judgment promote the commercial interests of the United States."
The Constitution, however, made no provision for a council of state, although soon after Washington took office, the Department of Foreign Affairs (July 27, 1789), renamed the Department of State (September 15, 1789), the War Department (August 7, 1789) and the Treasury Department (September 2, 1789) were created to help administer the new government. Treasury was given responsibility for business and commerce. The Secretaries of these departments and the Attorney General, who had been appointed under the act of September 24, 1789, became members of the first Cabinet.
From: https://www.commerce.gov/about/history/origins