Congress decided the election of 1800 primarily because:
- No candidate won the electoral vote.
In the election of 1800, Thomas Jefferson and Aaron Burr tied in the Electoral College with 73 votes each. Since no candidate received a majority of the electoral votes, it was required by the U.S. Constitution (specifically the 12th Amendment) that the election be decided by the House of Representatives.
The other options provided (popular vote tie and not enough citizens voting) are not accurate with respect to the reasons Congress was involved in deciding the election. The popular vote was not a factor since the system of popular votes was not uniformly established at that time and the issue was specifically related to the electoral vote.
So the correct reason for Congress deciding the election is primarily because no candidate won the electoral vote.