Think about "April 1861: The War Begins." Why did Alexander Hamilton Stephens believe that President Lincoln had "made the use of force necessary"?

This is because, President Lincoln has to interven after the fall of the fall of Fort Sumter of Carolina to the Union Confederates.

Explanation:

When the Fort of Sumter was captured, the President was jittery that the country was going to be divided and lose out on its unity stand just because of the slave trade issue.

He was so determined not to be remembered as the president that did nothing when secession plans where carried out by slave trade inclined States and to upholds the American constitution that, he has to take drastic action. Abraham Lincoln has no other option than to issue a proclamation calling for 75,000 volunteer soldiers to quell the Southern "insurrection."

This use of force was necessary because, it finally lead to the crushing of the dissenting states and unification of all the states together under one country.