Which critical election established the current democratic and republican parties as dominant within americas 2 party system?

The answer is election of 1860
The 1860 election happened when during the rise of major political groups that have differing principles.
The Republicans strongly support the abolishment of slavery while the democratic party support to keep the slavery system.
In the end , The Republican party (that led by Abraham Lincoln) won that election.

The nineteenth amendment changed voting rights as it allowed for women to vote nation wide