The Bald Eagle (Benjamin Franklin wanted it to be the turkey, but was outvoted.)

Because Lincoln's election as President meant there would be no new slave-states. So the South would always be outvoted in Congress, which would tend to pass laws that favoured the North over the South.
Because Lincoln had won the election of 1860 on a ticket of no new slave-states. So the South was doomed to be outvoted in Congress.

Some words that mean the same as minority include: the few, the outvoted and opposition. Depending on the situation, anyone can be a minority.

Lincoln's win in 1860 on a ticket of no new slave-states. This meant that the South would always be outvoted in Congress.

Made it difficult to create new slave-states, so the South always got outvoted in Congress.