Whigs they replaced was only 23 years old when it disappeared in 1856.
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I am not an American political historian (I am a medievalist), but from what I remember when the Republicans were founded there were only the Whigs and Democrats (making the Repubs a “third party”. With the rise of the Republican party, the Whigs disappeared, thus leaving us with only 2 parties again.
My impression is that it was almost an instant replacement “They were organized on February 28, 1854, held their first convention on July 6, and elected forty-four Representatives and fifteen Senators in November (19% of the House; 25% of the Senate)*.” by 1860 they had it all, Presidency, Senate, Congress. (There were real “third parties” back then to
Medved explains it but I don’t know his explanation, but it sure bears no resemblence with our 49 “third parties” today and of course the country and electorate are entirely different today, the Libertarians have been around almost 40 years and only have less than 226,000 registered members.