Because the constitution requires state and national government to be united, but each having it's own power. The constitution also states that no one person should have too much power, nor should any branch or state have too much power, so the power is split evenly.
SJ IEKDEKFKWFKKWDKWKDIWJXJXKD
The election of 1800 marked an election (the 4th US election) when the presidential control shifted to a different political party, and it was an advance in democracy.