It ought not to be for a moment forgotten, that the great conflict upon which we have now fully entered, is a struggle for the very existence of the United States Government. On one side is arrayed the doctrine of Secession—with its inevitable consequences of disintegration, disorder, lawlessness, public robbery, and repudiation of all obligations, public and private: on the other, is arrayed the Constitutional Government of the country, with its adjuncts of public order, obedience to law, security to property, and fidelity to all obligations. On the one side is an established and beneficent government, resting on the democratic principle of the will of the majority; on the other, is a disorganizing usurpation, resting on the ambition of a political faction, and deriving no authority whatever from the people. On the one side, is a free Constitution, consecrated by the patriot fathers of the Republic, and approved by seventy years of successful trial; on the other, is an odious innovation, hatched by a band of conspirators at Montgomery, whose chief end is the perpetuation and extension of human slavery. On the one side, is a government hitherto obeyed at home, and respected abroad; on the other is an upstart oligarchy, reluctantly submitted to within its own borders, and justly despised by every foreign power. On the one side, the struggle is unequivocally one for the rights of the people; on the other, it is just as plainly one for the supremacy of a slave propaganda.

Until within a brief period, the cause of this foul and hideous usurpation has not been without its advocates and apologists among us. Until it revealed its true character, in all its naked deformity, by the unprovoked and treasonable attack upon Fort Sumter, there were found those willing to extenuate and even to champion this great rebellion. We were told that secession was but an assertion of the doctrine of State Rights; that it was a vindication of the great principle of self government; that we “must not coerce the South,” and that a free people were not to be held in the Union by force. The cause of these Southern usurpers was likened to that of our revolutionary fathers taking up arms against the tyranny of Great Britian; and we were asked to “let the South go in peace,” and consent to a final separation of the Union. We were pointed, with shuddering finger, to “the horrors of civil war;” we were warned not to incur the guilt of “fratricidal strife,” and we were besought never to imbrue our hands in “fraternal blood.”

The roar of the remorseless cannon which sought the destruction o£ Major ANDERSON and his brave little garrison, who were starving under the folds of the Stars and Stripes, dissipated all these specious arguments into air. Up to that time the patient ear of the people had been drugged with the delusive idea that these rebels were asking only for their rights, and that a peaceful recognition of secession was all that was wanted to give repose to the country. But the wanton inauguration of war by this unholy league of usurpers tore the film from the eyes of the most confiding advocates of peace and conciliation. It aroused us all to an appreciation of the fact that we have an armed aggression—not a peaceful secession—to deal with. It convinced the most incredulous that the claims of JEFF. DAVIS & Co. could not be settled by any other than a bloody arbitrament. It proved that the policy which had been pursued by the Government—of steady inactivity—yielding and retiring in the face of a steady aggression, could have no other end than the ultimate destruction of the Government itself. It showed that the policy of peace toward an armed and determined enemy was a suicidal policy. And it convinced the nation that the question of the stability of our Government, which had hitherto been discussed only in calm debate, must be settled at last at the point of the sword, and by the thunder of cannon.

That we are not drifting causelessly into an appeal to force, will become palpable to any one who will reflect on the nature of the claims set up by this Southern usurpation. These claims, analyzed, are tantamount to the utter destruction of all government and social order. If their doctrine of secession, as illustrated and enforced by their practice, is true, then there is no such thing as governmental authority, or social obligation. If any minority has the right to break up the Government at pleasure, because they have not had their way, there is an end of all government. If any State may secede from the Union at pleasure, so may any county from the State, any town from the county, and any individual from the town. If we are to admit the right of a State to repudiate the constitutional obligations it has voluntarily assumed, there is an end of public faith, and all organizations for securing public order may at any moment dissolve into their original atoms. The good order of society, the operations of commerce, the interests of millions, are at the mercy of whatever league of factionists may attempt to resist the existing government, or to get up a new one. There is no disputing the fact that the necessary and legitimate corollary of the doctrine of secession is anarchy.

If these things are so, then it follows irresistibly, that there must somewhere be lodged a power to prevent such disintegration and disorder, to enforce the public will, as manifested in law, and to vindicate the right of the Government to obedience. That power is clearly vested by the Constitution in the national Executive. He is to call forth the militia of the country to suppress insurrection against lawful authority. His power to do this has been further defined by Congress, requiring him, whenever the laws shall be opposed, or the execution of them obstructed, in any State, by combinations too powerful to be suppressed by judicial proceedings, to use the militia to suppress such combinations, and to cause the laws to be duly executed.

That emergency has clearly now arisen. The unlawful combinations which have broken the national laws, stolen the national property, undertaken to collect and appropriate the national revenue, and taken up arms against the national Government, must be put down by the strong arm of power, or they will go on in their career of conquest, until they have seized everything belonging to the Government, and made a prize of the Government itself. Those who are fighting in this contest, for the rightful supremacy of the Government, are fighting for the maintenance of the Republic, as well as for the security of their own dearest interests. They are fighting the battle of republican liberty, against the foulest and most treacherous usurpation and tyranny. They are fighting for constitutional law and the faith of compacts, against anarchy and repudiation. They are fighting for the supremacy of the popular will, against the self-constituted despotism of a miserable minority. The struggle in which we are engaged is a battle between good citizens and traitors—between honest men and repudiators, between law and disorder, between education and ignorance, between democracy and despotism.

A surrender to Secession is the suicide of government. There is no one capable of putting two ideas together, but must admit the truth of this proposition. If we succumb to secession now—if we suffer these insurgents and usurpers to dictate to us the terms of a national dismemberment, our national government is gone—hopelessly, irretrievably gone. We shall never more have peace or public order at home—we shall never more lift our head among the nations of the earth. The great battle which is now joined, is to prove whether a Republic, founded on the will of the people, is capable of exerting power enough to enforce its laws and maintain its existence, or whether it contains within itself the seeds of its own destruction.

If we succeed, we shall have vindicated the great principle of the rule of the majority, and restored the distracted country to a peace and prosperity never before enjoyed. The elements which have produced this outbreak, which have kept us in continual terror of dissolution, will have proved their strength or weakness, and thereafter will weigh only at their real value. We shall have preserved from swift destruction the best and freest Government the world has ever seen, and we shall have saved our children from the unspeakable misfortune of becoming the citizens of an anarchy or a despotism.

If we fail—but we will not yield, even for one moment, to so melancholy and disheartening an anticipation as failure—a failure which would cost us all in life that is worth living for, entail upon our children a lasting heritage of shame, and postpone for ages the progress of mankind. We shall not fail. The cause is too just and too glorious, and its vindication is committed to the charge of too many stout hearts and hands. Whatever there is of public virtue—of popular liberty—of national respect—whatever of faith in liberal institutions—whatever of faith in human progress—in the hopes of mankind—all—all are pledged to our side of this great struggle. We are living in the presence of events of startling significance, and amid a conflict of principles more mighty than the page of history records. The eyes of the world are upon us. The moral forces involved in the contest are even more stupendous than the material. By all the motives that have urgency upon human conduct, we are called upon not to frustrate the fair promise of ages. By the duty we owe to an imperilled Government—by our fidelity to freedom and the rule of the people—by all the obligations of public and private faith—by the good name of our Republic, on trial before all the world—by our interests, as citizens, in the security of commerce, property and public order—by the love of liberty, that springs immortal in the human breast, by the hopes of our children, by our homes and firesides, and the bones of our fathers that are under the ground—WE MUST CONQUER.