Have you ever wondered why the two parties are split so evenly? In America we have the Democratic and the Republican parties and they are so evenly balanced. It seems bizarre almost that it should work out to be so close. There's a good reason it does, we want it to be.
There are a couple things in place that ensure that the two parties stay balanced.
The Middle of the Road
Despite what it may seem like, they are a very significant number of people whose political beliefs are a mixed bag of things from both 'Democratic' and 'Republican' beliefs. There are plenty of people who are fiscally liberal and morally conservative, people who are fiscally conservative and morally liberal, or so many other things.
These people are the key group in what keeps the parties balanced.
Parties don't like to be losing
Nobody likes to be the inferior party. So when a party finds itself to be the losing party, they adjust their stance on issues to reclaim people they lost and gain new followers they never had. They find an issue that they're really losing people on and swap their stance on it. It's very easy to do. Since a party is comprised of it's elected officials (or campaigning individuals), they just swap their stances over the course of an election season and the zeitgeist that comes out the other side is the new party stance. TADA!
This is what we call progress.
