3. What greatest concern or emergency was mentioned by Lincoln in his speech?

The greatest concern or emergency that was mentioned by Lincoln in his speech was about democracy and how it was self-sustaining.

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Lincoln described the dangers of the Union that get dissolved over slavery. Also, the dangers of the union that get dissolved over slavery rallied northern Republicans.

Explanation:

Lincoln described the dangers of the Union that get dissolved over slavery. Also, the dangers of the union that get dissolved over slavery rallied northern Republicans. The most crucial part of the speech is ''A house divided against itself cannot stand. I believe this government cannot endure, permanently, half slave and half free''

b. the colonies must seek protection from other nations.