Which event helped to shape the partisan patterns of the North and South for nearly a century?

The Civil War

The first answer is certainly correct, however, as a minor edit, the various Reconstruction Acts and their implementation also helped shape partisan politics & patterns between Northern and former Southern Confederate states.

Both the Civil War and Reconstruction were dominated by Republicans and most of their views on slavery and the Southern rebellion, the Civil War. Many people for generations afterward, had a strong dislike for the Republican party and elections for public office were almost a one sided affair in the South. They voted for Democrat party candidates in almost all levels of government. So much so that the term "solid South" meant that Democrats could count on Southern support in elections. Even after many decades had passed the South blamed the Republican party for the federal policies that were seen as detrimental to the South.