Why did political parties emerge in the 1790s?

The roots of the political parties lie in the Constitutional Convention. During the convention, many delegates favored a strong national government that resembled Britain's. This group was called the Federalists. On the other hand, many delegates felt that a large national government would become corrupt were worried about similarities to the British government from whom they had recently won independence. This group was called the Anti-Federalists.

The Constitution was ratified, and George Washington became the first president unanimously. His cabinet held members who represented starkly different views however. His Secretary of the Treasury was Alexander Hamilton, one of the most vocal and extreme Federalists. His Secretary of State was Thomas Jefferson, who often talked of limiting the Constitution and expanding state and individual rights.

The supporters of each cabinet member and their ideas coalesced into political parties leading up to the 1792 Congressional Elections (both parties supported George Washington for reelection).

Hamilton's supporters consisted mostly of those who had supported the expanded Constitution during the convention, and continued to identify themselves as Federalists. Jefferson's supporters (who had never identified by the name Anti-Federalists) consisted of the delegates who opposed Hamilton in the convention as well as the many people who felt isolated by Hamilton-led policies during Washington's first four years. They identified as the Democratic-Republicans.

The division became increasingly tense after Washington announced that he would not run for reelection in 1796 (setting the two term precedent). John Adams ran against Jefferson, each representing the different parties.