The Alabama Constitution
apportioned representatives to the State legislature based on county.
Since some counties had a lot more residents than other counties did, that
meant that a representative from a rural district would represent the
interests of a few residents, while those from urban districts represented
the interests of a lot of residents.
Sims and some other Alabama
residents sued, claiming that the apportionment was a violation of the Equal
Protection Clause of the 14th
Amendment.
Basically, they argued that
a few hundred people in two rural counties would get more votes in the
Legislature than thousands of people living in one urban county.
That's known as malapportionment.
The US Supreme Court struck
down the Alabama apportionment plan.
The US Supreme Court found
that, based on the Equal Protection Clause, everyone's vote should count for roughly the same amount.
Therefore all voting districts have to be roughly equal in proportion.
Alabama had argued that
their apportionment plan was designed to balance the interests of urban
cities with those of rural farms. However, the Court found that, "Legislators
represent people, not trees or acres. Legislators are elected by voters,
not farms or cities or economic interests."
This case established the
principle of "one person, one vote."
Btw, Justice Earl Warren
later wrote that this was the most important decision he ever made on the
Supreme Court.