Answer:
The Federalists supported the new U.S Constitution and fought to replace the Articles of Confederation because the Articles of Confederation were weak and caused disruption in the newly independent United States.
The Articles of Confederation had a weak central government (because of the fear of the British monarchy), had no national currency, and lots of other issues. This caused chaos in the US. The 13 independent states were basically allies in a "confederation" and not united. Each state had their own currency and the federal government couldn't raise taxes and had no real power.
This lead to a poorly formed United States of America that just got independence.
The Federalists wanted to fix these issues that the Articles of Confederation failed to address, but in order to do that, they supported a <em>strong</em> federal government (even if it was run by the people). Of course, the people who supported the Articles objected to this (because of the fear of tyranny). To compromise, the Federalists wrote a Bill of Rights to protect the rights of citizens and states from the new federal government.
The Federalists did solve the issue of a national currency, federal power, and taxes. Once the US Constitution was set in place, the federal government and the US was doing better than it was back with the Articles.
Fun Fact: When the representatives were meeting to make the US Constitution, they broke the law because the Articles of Confederation forbid this. You could only revise the Articles, not write a completely separate and new document.
Hoped this helped!
