Final answer:
Between 1854 and 1861, the area of slave states and territories open to slavery changed due to the Kansas-Nebraska Act, the addition of new slave states, and the Dred Scott decision.
Step-by-step explanation:
Between 1854 and 1861, the area of slave states and territories open to slavery changed due to several factors and events.
1. Kansas-Nebraska Act: In 1854, the Kansas-Nebraska Act was passed, which allowed the residents of these territories to decide whether slavery would be allowed locally. This led to a violent conflict known as 'Bleeding Kansas' between pro-slavery and anti-slavery forces.
2. Increased Slave States: During this period, new slave states were added to the Union. For example, in 1858, Minnesota was admitted as a free state, while in 1859, Oregon was admitted as a free state. On the other hand, in 1858, Kansas was admitted as a slave state.
3. Dred Scott Decision: In 1857, the Supreme Court ruled in the Dred Scott v. Sandford case that enslaved African Americans were considered property and could not be granted freedom even if they lived in free territories. This decision further expanded the area open to slavery.