Why did George Washington feel it important to keep the country united?

In his farewell address, George Washington had two pieces of advice for the American people: to stay away from the factionalism of political parties and to avoid foreign alliances.
Even during his second term Washington began to see the rise of political parties in his own cabinet as Thomas Jefferson and Alexander Hamilton began to view the role of government differently, and they began to cultivate followers. Washington knew that the United States was a republican experiment and that many other governments throughout history had gone through civil war due to factionalism. Washington, like the other Founding Fathers, was aware of the strife that afflicted the Italian city-states during the Renaissance and the divisions of ancient Rome and Greece. Washington knew that factionalism could lead to civil war and most governments emerged from these in a state of vulnerability that could possibly lead to outside takeover. Washington's advice to avoid factionalism and political parties in general was an attempt to get Americans to sort out their differences and reach a consensus rather than see politics as a game with winners and losers. Washington could not stop the rise of parties: the two-party system was in effect in the third presidential election and has been a staple of American political life ever since.