Why are you suddenly surprised to learn that?
And lacking the votes, northern states did the next best thing - took up an army to overthrow the constitution’s slavery provisions, often popularized “as He died to make men holy let us die to make men free.”
No, they took up an army to fight the war that the South forced upon them.
Northern states taking up an army to overthrow the US constitution had an added benefit - the opportunity to destroy - kill you might say - economic and political rivals in the south.
How exactly did they "overthrow the U.S. Constitution"?
When you say “No”, do you mean the North did not fight to “free the slaves.?”
The song, Battle Hymn of the Republic, which is the topic of this thread, states otherwise. The song gives one clear reason for the war: “As He died to make men holy let us die to make men free.” The song actually says little about using federal ports to collect import taxes.
Many millions of people then and now have sung the song vigorously believing the valorous union army was fighting to "free the slaves." If that is not correct, then we can dismiss the notion the North fought for some high moral purposed like ending slavery.
Of course, if the North was fighting because it was in the North's economic and political best self-interest, then, arguably, that was a high moral cause worth killing 600,000 people.
And how did the South force a war upon them? What vital Northern interest did the South threaten?
Did they take up residence in a fortress overlooking New York Harbor from whence they could threaten shipping if they were of a mind to do so?