First of all, the word "tyranny" isn't in there. Second of all, "tyranny" is a matter of perspective. The Philippines considered us tyrants when we were running that country.
Lincoln had previously supported the right of Texas to become independent of Mexico. Apparently he was against the right of Texas to be independent of him.
The fact of history remains that neither President Buchanan nor President Lincoln lifted a finger to prevent Deep South states from first declaring secession, then forming a Confederacy, establishing a Confederate constitution, Confederate national government & military forces.
Both only acted (Buchanan ineffectively) to stop Confederate aggression against the United States.
Both Democrat Buchanan and Republican Lincoln believed that unapproved unilateral declarations of secession were wrong, legally, but neither believed the United States could take military actions on that basis alone.
So Civil War was not the result of declarations of secession, but rather of Confederate aggression against the United States.