Final answer:
The Missouri Compromise was declared unconstitutional for infringing on Congress's power to ban slavery in territories. This ruling directly impacted Dred Scott's citizenship, as the Supreme Court denied his claim to freedom and established that Blacks could not be US citizens.
Step-by-step explanation:
The Missouri Compromise was declared unconstitutional due to its infringement on Congress's authority to bar slavery in territories. The compromise aimed to maintain a balance between free and slave states by prohibiting slavery in certain territories. However, the Supreme Court ruling in Dred Scott v. Sandford declared that Congress did not have the power to ban slavery in any territory, thereby invalidating the Missouri Compromise.
This unconstitutional compromise had a direct relationship to Dred Scott's citizenship. In his lawsuit, Dred Scott argued that his residence in a free territory made him free and entitled him to sue in federal court.
However, the Supreme Court ruled that Blacks, including Scott, could not be citizens of the United States. This decision denied Scott's claim to freedom and reinforced the institution of slavery.