What shared beliefs and experiences enabled them to keep the nation together, despite their deep disagreements?
Despite their differences, the Republicans and the Federalists always agreed with the fact that the new Constitution was needed because the Articles of Confederation caused a series of troubles because of the lack of a central government. The Constitution came in 1788 and this new country needed to become strong in the eyes of other countries. This was the main purpose that united both Republicans and Federalists. In 1800s Presidential power switched hands to the Republican party with the win of Jefferson, who said in his inauguration that “We are all Republicans, we are all Federalists”.
Was there ever a serious danger that the new federal government could have collapsed in civil war?
Yes, if the Confederacy won the war the new federal government would have collapsed because there would be a huge possibility for other states to leave the Union.