Lastly, the Union was and is still the possessor of Territories not included in any State, and in the Territories, whatever subordinate self-government they might be allowed, the Federal authority has always been supreme and uncontrolled in all matters. But as these Territories have become more settled and more populated, portions of them have steadily from the first been organised as States and admitted to the Union. It is for Congress to settle the time of their admission and to make any conditions in regard to their Constitutions as States. But when once admitted as States they have thenceforward the full rights of the original States. Within all the Territories, while they remained under its jurisdiction it lay with Congress to determine whether slavery should be lawful or not, and, when any portion of them was ripe for admission to the Union as a State, Congress could insist that the new State's Constitution should or should not prohibit slavery. When the Constitution of the Union was being settled, slavery was the subject of most careful compromise; but in any union formed between slave States and free, a bitter root of controversy must have remained, and the opening through which controversy actually returned was provided by the Territories. On all other matters the makers of the Constitution had in the highest temper of statesmanship found a way round seemingly insuperable difficulties. The whole attitude of "the fathers" towards slavery is a question of some consequence to a biographer of Lincoln, and we shall return to it in a little while. 2. _Territorial Expansion_. A machine of government had been created, and we are shortly to consider how it was got to work. But the large dominion to be governed had to be settled, and its area was about to undergo an enormous expansion. It will be convenient at this point to mark the stages of this development.