Slavery that is. Apparently an historian once asked why Abraham Lincoln had chosen to highlight the divisive issue of slavery over so many other important issues facing the country:
"With all the problems that might have been put before the people as proper matter for their consideration in choosing a senator —choice of government servants, immigration, the tariff, international policy, promotion of education, westward extension of railroads, the opening of new lands for homesteads, protection against greedy exploitation of those lands ... encouragement to settlers ... improving the condition of factory workers, and alleviating those agrarian grievances that were to plague the coming decades—with such issues facing the country, those two candidates for the Senate talked as if there were only one issue."
Hadley Arkes posts that paragraph today in an article today at The Catholic Thing and answers why slavery was not just one issue among many:
"As Harry Jaffa pointed out, following Lincoln, the question of whether a black man was a human being was not a 'value judgment.' His standing as a human would not depend on whether we imputed 'value' to his life. Whether he was a 'human' was a question with an objective answer. That answer did not hinge on the vote of a majority; the answer had to be clear before we would know just what kinds of creatures are suited for the life of politics in offering arguments and reasons and casting votes."
Arkes argues the same question and importance is involved in today's abortion debate. See the whole article.