Final answer:
President Buchanan did not move to block the southern states from seceding mainly because he sought to preserve the Union.
Step-by-step explanation:
President Buchanan did not move to block the southern states from seceding mainly because he sought to preserve the Union. While he recognized the right of the southern states to secede, he believed that the Union should be perpetual and that preservation of the alliance was more important than states' rights. He hoped to encourage compromise between the North and the South before leaving office.