Final answer:
The American Civil War occurred during the Civil War Period, from 1861 to 1865, making option d) Civil War Period the correct answer.
Step-by-step explanation:
The historical event known as the American Civil War took place during the Civil War Period. This conflict was fought between the northern states (Union forces) and the southern states (Confederacy) from 1861 to 1865 over the question of slavery and states' rights. The Civil War began with the firing on Fort Sumter in South Carolina on April 12, 1861, and ended with the surrender at Appomattox Courthouse in Virginia on April 9, 1865. The correct answer to the question, 'In which period did the following historical person/event happen: American Civil War?' is thus d) Civil War Period.