Slavery, thus intrenched in the midst of such powerful allies, and without competition in tropical cultivation, has become the sole reliance of KING COTTON. Lest the sources of his aggrandisement should be assailed, we can well imagine him as being engaged constantly, in devising new questions of agitation, to divert the public from all attempts to abandon free trade and restore the protective policy. He now finds an ample source of security, in this respect, in agitating the question of slavery extension. This exciting topic, as we have said, serves to keep politicians of the abolition school at the North in his constant employ. But for the agitation of this subject, few of these men would succeed in obtaining the suffrages of the people. Wedded to England's free trade policy, their votes in Congress, on all questions affecting the tariff, are always in perfect harmony with Southern interests, and work no mischief to the system of slavery. If Kansas comes into the Union as a slave State, he is secure in the political power it will give him in Congress; but if it is received as a free State, it will still be tributary to him, as a source from whence to draw provisions to feed his slaves. Nor does it matter much which way the controversy is decided, so long as all agree not to disturb slavery in the States where it is already established by law. Could KING COTTON be assured that this position will not be abandoned, he would care little about slavery in Kansas; but he knows full well that the public sentiment in the North is adverse to the system, and that the present race of politicians may readily be displaced by others who will pledge themselves to its overthrow in all the States of the Union, Hence he wills to retain the power over the question in his own hands.