Liberty of beneficent spirit not military might constitutes a Free Republic (with good defense system to guard against infiltration).

What constitutes the bulwark of our own liberty and independence? It is not our frowning battlements, our bristling sea coasts, the guns of our war steamers, or the strength of our gallant and disciplined army. These are not our reliance against a resumption of tyranny in our fair land. All of them may be turned against our liberties, without making us stronger or weaker for the struggle. Our reliance is in the love of liberty which God has planted in our bosoms. Our defense is in the preservation of the spirit which prizes liberty as the heritage of all men, in all lands, every where. Destroy this spirit, and you have planted the seeds of despotism around your own doors.
--September 11, 1858 Speech at Edwardsville

It is your business to rise up and preserve the Union and liberty, for yourselves, and not for me. I desire they shall be constitutionally preserved.
--February 11, 1861 Reply to Governor Morton

It is not merely for to-day, but for all time to come that we should perpetuate for our children's children this great and free government, which we have enjoyed all our lives. I beg you to remember this, not merely for my sake, but for yours. I happen temporarily to occupy this big White House. I am a living witness that any one of your children may look to come here as my father's child has. It is in order that each of you may have through this free government which we have enjoyed, an open field and a fair chance for your industry, enterprise and intelligence; that you may all have equal privileges in the race of life, with all its desirable human aspirations. It is for this the struggle should be maintained, that we may not lose our birthright--not only for one, but for two or three years. The nation is worth fighting for, to secure such an inestimable jewel.
--August 22, 1864 Speech to the 166th Ohio Regimen