The national government got stronger thanks to the Articles of Confederation being replaced with the US Constitution. The Articles of Confederation was America's first constitution. This constitution lasted roughly a decade, as it was extremely ineffective and gave the federal government very little power. For example, the federal government could not collect taxes or force states to follow national laws.
When the US Constitution was passed, the federal government gained significant power. This included the creation of an executive branch, the idea that federal laws trump state laws, and the ability to raise funds in order to create a national military.
