It is very clear that if the secessionists, in their madness, insist upon a blockade of the Mississippi river, a bloody conflict must be the result. The potent voice of the Northwest, speaking by the tongue of a democratic member from Illinois, (Mr. McClernand,) has already declared that the free people who inhabit the region of the Mississippi Valley will never consent to the destruction of their commerce. As an echo to this emphatic declaration in Congress, the unanimous expression of the press of the West and Northwest is that of a fixed resolution to resist such encroachments upon guarantied rights and privileges. “Will an empire of ten million people in the West be content to become subordinate—a nation of herdsmen? Perish rather;” said Mr. McClernand in the House. “The slightest obstruction or annoyance offered by real or pretended sovereignties to navigation upon the mighty thoroughfare of northwestern commerce would arouse a spirit that would cut its way to and through the mouths of the Mississippi, or sacrifice tens of thousands of lives in the attempt,” is the language of the Louisville Journal, speaking in behalf of the commerce of the Ohio.

These are significant indications of the temper of the West. They are not to be lightly disregarded. But a week has elapsed since batteries were planted under the Vicksburg Hill, on the bank of the Mississippi, for the avowed purpose of stopping the boats engaged in the navigation of the river. The act was done by the order of Governor Pettus, who takes this course to assert the sovereignty of his state, just as Governor Pickens ordered the batteries at Morris Island to fire upon the Star of the West, by way of showing how brave his state could be when there was no fear of resistance. The order to bring—to all passing vessels on the Mississippi, appears to have been immediately obeyed, for we publish elsewhere an account of some deeds of this nature. The war is therefore opened, and the trouble may be expected to reach a crisis in a few days.

Looking for a moment at the effect of a continuance of this repressive policy, we see the terrible evils that are likely to grow out of it. The commerce of the Mississippi itself is not the only interest involved. The gigantic tributaries of that artery of trade are no less blocked. Of what use is the Missouri, draining the vast territory to the westward of the Mississippi, if the blockade of the latter is maintained? What will become of the millions of tons of western produce and manufactures that find an outlet through the Ohio river, if the Mississippi outlet is sealed? Whither can the westward freight of the Lakes find its way? The West, with its lusty strength, depends upon the tributary streams that flow into the Mississippi for the conveyance of its produce to paying markets. With these untrammeled and with the grand outlet free, the rich Valley grows and knits itself more firmly together. With these arteries congested, its strength would decay and its life dwindle. It is not a matter of wonder that a general shout of execration goes up against the tyranny of the traitors whose love of despotism has led them to commit an infamous outrage.

We warn the Louisianians and Mississippians that if they persist in their senseless folly, the upshot of the southwestern secession will be much more serious to themselves than that of South Carolina is likely to be. The West will take the remedy in its own hands, President or no President. Mr. Buchanan may tamper as he pleases with the traitors in Charleston and Savannah. He may permit the public property to be seized and held by rebels. But the West will never ask his consent to rid itself of an obstruction which threatens to arrest its very life-currents. Years ago, when the Spanish dominion was established in the southwest, the people of the valley of the Mississippi were ready to fly to arms to secure the free navigation of their river; and now, when the population of the Northwest exceeds that of all the slave states, they are more than ever ready to fight.