With the effect of Lincoln's plans to reunify the country, the start of the Reconstruction era, when former Southern rebel states were reintegrated into the Union, is the cause.
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The Reconstruction era, which lasted from 1865 to 1877 after the American Civil War, saw the country struggle to decide how to treat African Americans legally and to reintegrate the seceded states into the Union.As ordered by Congress, Reconstruction removed the last vestiges of Confederate secession in the Southern states while also abolishing slavery. Reconstruction also refers to Congress's overall effort to change the 11 former Confederate states and the Union states' contribution to that change.
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I believe the answer is A according to my calculations.
The leader of Great Britain's government is the Prime Minister