Why was the capture of Atlanta important to Lincolns reelection?

Answer 1

Because Atlanta was an important strategic an logistic objective, whose conquest would be crucial from not only a military but also a political point of view, for the presidential elections were approaching.

That meant that a great victory was essential to raise the morale of the public of the north and to restore the consents towards Lincoln Administration.

Last but not least it was expected that the Confederates would have hardly fought to prevent Atlanta from being conquered, thus giving the opportunity to the superior Union Armies to destroy or scatter the Confederate Army of Tennessee.

All the aforesaid goals were achieved, giving then the way to Sherman Army to plan and develop the decisive military campaign called the March to the Sea.

Answer 2

Because it was a railroad hub. Railroads were the vital, indispensable and only means of moving supplies to the front to support the army, other than by water. The rivers in the south were mostly unusable for such transport, leaving only the railroads. Several rail lines crossed in Atlanta, which had caused its astoundingly rapid growth - the city did not exist before 1837 and twenty-five years later was one of the largest in the south. There was also some important industry there, but Atlanta's primary importance was as a transportation center.