Early American leaders thought that the head of the British government, the king, had too much power. Because of this, they limited the powers of the head of the new U.S. government. They decided that the people would elect the president every four years.
The president is the only official elected by the entire country through the Electoral College. The Electoral College is a process that was designed by the writers of the Constitution to select presidents. It came from a compromise between the president being elected directly by the people and the president being chosen by Congress. Citizens vote for electors, who then choose the president. Before 1951, there was no limit on the number of terms a president could serve. With the 22nd Amendment to the Constitution, the president can only be elected to two terms (four years each) for a total of eight years.