Lincoln was trying to appeal to Southern voters by picking Andrew Johnson as his running mate. These two men were actually very different politically speaking. Lincoln was a Republican, Andrew Johnson was a Democrat. Lincoln was from the Midwest US, Andrew Johnson was from Tennessee.
Lincoln knew that having a Democratic Vice President who once represented a Confederate state (Tennessee) would allow his presidency to appeal to a wider range of voters.
President Roosevelt saw support from the Allies involved in World War II
increase due to his strong victory during the 1940 Presidential
election, where he easily defeated Wendell Willkie
The compromise counted three out of every five slaves as people, giving the Southern states a third more seats in Congress and a third more electoral votes. The Southerners were using their slaves to their advantage politically.
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