What is federalism? How is this idea related to the Constitutional Convention?

Federalism is the division of powers between the states and the federal government under the United States government, established by the Philadelphia Convention of 1787. Prior to this convention, the United States struggled with a number of urgent concerns that were difficult to resolve under the Articles of Confederation, which proved a weak national government with few coercive powers over the states. The Constitution that emerged from the debates at the Philadelphia Convention was intended to address these issues without completely negating the powers of the states (or, for that matter, individual liberties.) The system developed through a number of debates at the Convention has become known as "federalism." Under this system, the national government is supreme. This is established clearly in the Constitution. The national legislature is given such powers as printing and coining money, entering into treaties, and many others that were deemed essential for the new nation to function as a unified country. The states were denied these powers. At the same time, many powers were shared—the power to tax, for instance, was given to both levels of government. These powers have become known as concurrent powers. States also reserved powers not granted to the federal government. So within this system, the supreme federal government has powers delegated to it, and the states have their own powers. Later certain powers of the states were protected under the Bill of Rights, which placed restrictions on the power of Congress. This, in short, is the system known as federalism. Debates over the relative extent of these powers have always been, and remain, central to American politics.
https://constitutioncenter.org/learn/hall-pass/federalism