The writing of the Constitution of the United States, which supplanted the Articles of Confederation, changed the US political system in important ways. Let us look at the two most important ways in which it did this.
First, the Constitution took much more power for the federal government and away from the states. The Articles of Confederation had created a system in which the states had all the power. The Constitution changed this. It created a national government with a strong executive. It made the laws passed by the national government supreme, giving them precedence over laws passed by the states. It gave the national government the power to tax and to regulate commerce between the states. All of these were powers the national government did not previously have.
Second, the Constitution set up a system in which the powers of the government would be divided between various branches. The national government under the Articles of Confederation had essentially consisted only of a legislative branch. The Constitution changed this, making a bicameral legislature and creating strong executive and judicial branches.
In these ways, the new constitution changed the American political system in important ways.