The correct answer to this open question is the following.
Although there are no options attached we can answer the following.
The major U.S. War that helped change the laws that stated that enslaved Africans were not U.S. Citizens was the American Civil War (1861-1865).
Before the Civil War, slavery was the normal thing in the large plantations of the southern states. Indeed, the economy of the South totally depended on slaves to produce the kinds of crops that had to be exported to Europe.
During the war, U.S. War, US President Abraham Lincoln issued the Emancipation Proclamation in January 1863, stating that al slaves in the south had to be free.
After the war, and during the Reconstruction period, white people established a series of laws called the Jim Crow laws that limited black people's rights.
It was the 14th Amendment to the United States Constitution granted citizenship to all the people born in the US or that were naturalized in the US, as was teh as of most black people.
