The year 1808, fixed by the Constitution as the limit of the duration of the slave-trade, witnessed the next contest. The result was a definite prohibition of the trade by law. But it was a barren victory for the cause of humanity. The interests involved in both Northern and Southern States had grown so large and influential as to make the law a dead letter. The trade continued with unabated vigour, and marked by even greater cruelties to the wretched cargoes. The Slave Power was growing in strength and determination, bent on controlling the national government, influencing our foreign relations, reaching out already to grasp new slave territory. From 1818 to 1821 continued the great contest over the admission of Missouri as a slave State, in which was involved the question whether the extension and encouragement of slavery was to be the permanent policy of the United States government. Men and words were not wanting to expose and condemn the contemplated evil. But the Slave Power had grown to too great proportions. Henry Clay, who had believed "slavery to be a wrong, a grievous wrong, which no contingency can make right," now, at the behest of slaveholders, threw his great influence against the cause of humanity. As in the days of the Constitutional Convention the Slave Power had secured the perpetuation of its system by threats of preventing a union of the States, so in 1821 it obtained the principle of the extension of slavery by threats of dissolving the Union. Thomas Jefferson, so faithful an advocate of freedom, was now appalled by the sound of a strife which, "like the fire-bell at midnight," announced disaster, and he counselled concession. Even John Quincy Adams was on the same side, "from extreme unwillingness to put the Union in hazard." So passed the so-called Compromise, which allowed slavery to break its bounds and to spread over Arkansas and Missouri. The Slave Power had won a great victory and had shown immense growth. The old apologetic position that the system, although wrong, could not be abolished without entailing greater evils, was now exchanged for the bold doctrine that slavery was a good thing, to be extended and strengthened. The struggle was growing fiercer and was becoming more clearly an issue between North and South, but the bone of contention was yet the extension, not the abolition, of slavery. The Slave Power, warned by the opposition it had met with in Congress, that a new spirit was arising in the North, instinctively felt that its position could be maintained only by further aggression. None but slaveholders were allowed to represent the South in Congress, where every public measure was considered first in the light of its effect upon the institution of slavery. At home, such humane laws regarding the blacks as still existed were repealed, new and more cruel enactments were passed, the manumission of slaves by grateful or repentant masters was prohibited.