That isn't a historical certainty. Even leaving the social axis aside and sticking strictly to economics, the American party system only started to fit a left/right model during FDR's presidency. Progressive Republicans started to split from the party in the '20s and eventually found themselves a home in the New Deal coalition. The big change of the post-Carter epoch is that the socially conservative, economically liberal "Reagan Democrats" have almost entirely disappeared off the map, resulting in both parties becoming more separate on social issues.
I think it's safe to say that a modern representative democracy (assuming a capitalist, industrialized society) will generally have a right faction and a left faction in national politics. What makes things complicated is when you throw in regionalism, nationalism, militarism, ethnic issues, moral issues, and any other matter of controversy that doesn't always split the same way as left/right economic positions.
I think it's safe to say that a modern representative democracy (assuming a capitalist, industrialized society) will generally have a right faction and a left faction in national politics. What makes things complicated is when you throw in regionalism, nationalism, militarism, ethnic issues, moral issues, and any other matter of controversy that doesn't always split the same way as left/right economic positions.