Regarding polarization, the two parties in the USA used to be regional, not conservative / liberal.
I think the polarization is largely due to the alignment of the parties to the most fundamental differentiation of philosophies - conservative versus liberal.
No one aligns %100 with either party, imho, gratefully.
Well they were regional, but also ideological at the same time. If you're talking about pre-Civil War, Southerners were more against a powerful federal government, Northerners were more in favor of it. And it wasn't just on the slavery issue. Even far before slavery as an issue started boiling over, they were fighting about the National Bank. Southerners tended to hate the bank because they were farmers (along Jefferson's yeoman farmer idea) and thought of themselves as independent and didn't like banks controlling inflation, while Northerners liked banks because the North was industry-oriented. They had different ideologies because they had different living conditions. You had people that were more agrarian and people who were more urban.
But even then you had Northern Whigs and Southern Whigs, and Northern Democrats and Southern Democrats, and that made politics national. There were even big third party constituencies that varied from region to region. On the eve of when the Civil War erupted the national Whig and Democrat coalitions fell apart, and that's when it became region vs. region.
Modern conservative/liberal politics likewise has followed regional lines for a long time.
But that isn't really the issue. The real point is that politics a long time ago was less institutional. Parties and coalitions could rise and fall. We had three party systems in the 19th century. In the 20th century we had one. When the media feeds into the perception of polarization it ends up creating it, and that just gives power to party bosses and institutional politics.