"This increasing unification has well-nigh obliterated State lines so far as concerns many relations of life. Yet, in a country of such enormous expanse, there must always be certain regional differences in social outlook and economic thought. The most familiar illustration of this is found in the history of slavery. The Constitution did not interfere with slavery, except to fix a time when the foreign slave trade should be abolished. Yet within a generation the country was confronting a sharp sectional division on this issue. Changing economic conditions made slavery profitable in the south, but left it unprofitable in the north. The resulting war might have been avoided if the south had adopted a policy of ultimate abolition. But as this method was not pursued the differences grew sharper until they brought on the great conflict."