The issue was first brought to a head in 1820, when Missouri sought to join the union as a slave state. After a heated debate, Congress passed the Missouri Compromise, which admitted Missouri as a slave state but also prohibited slavery in the rest of the Louisiana Territory north of the 36°30′ parallel. The Missouri Compromise temporarily resolved the issue, but it also deepened the divide between the North and the South and set the stage for future conflicts.
In the 1850s, the issue of new states was again brought to the fore by the Mexican-American War. The United States acquired a vast amount of territory as a result of the war, and the question arose of whether these territories would be admitted as free or slave states. The debate was particularly heated over the Kansas-Nebraska Act of 1854, which allowed the people of Kansas and Nebraska to decide for themselves whether they would be free or slave states. This led to a wave of violence in Kansas, known as "Bleeding Kansas," and further intensified the debate over slavery and states' rights.
The issue of new states was one of the main factors that led to the Civil War. In 1861, the Southern states seceded from the union and formed the Confederate States of America. One of the main reasons for secession was the Southern states' fear that the North would eventually gain enough power to abolish slavery. The Civil War was fought over the issues of slavery and state's rights, and it ended with the victory of the North and the abolition of slavery.
The question of new states and the balance of power between free and slave states was a complex and contentious issue that had a profound impact on the history of the United States. It was a key factor in the Civil War, and it continues to be a source of debate today.