Final answer:
The 'Doctrine of Necessity' represents Abraham Lincoln's belief in preserving the Union above all, even if it required temporary compromise on slavery. It was a guiding principle in Lincoln's presidency during the Civil War, underscoring the importance of the Union's permanence and integrity over the immediate resolution of the slavery issue.
Step-by-step explanation:
The "Doctrine of Necessity" that Abraham Lincoln refers to is the principle which justified his actions to preserve the Union above all else, even if it meant compromising on slavery issues. Lincoln's position was clarified in his responses to various correspondents and political interactions, where he consistently indicated that while he personally wished for the abolition of slavery, his primary goal during the Civil War was to save the Union.
This pragmatic approach to the political crisis of the time suggests that Lincoln was willing to endorse any measure under the Constitution that would hold the nation together, even if it meant that the abolition of slavery might not be immediate or complete.
The Doctrine of Necessity highlights the sometimes difficult choices Lincoln faced as he navigated between conflicting pressures and pursued both his personal beliefs and his duty as President to maintain the integrity of the United States.