Two-party question

[asterroc]

What is it about the US's three branches of government that has led to a two-party system throughout the US's history, where nations with two branches tend to have a robust multi-party system?

(Where by "two branches" I mean the Executive and Legislative merged into a Parliament and the head of their majority party is the prime Prime Minister. If there's another name for this style of government, I'd be curious to know.)

Comments

[q10.livejournal.com]

which ones are you thinking of? there are certainly some major ones (i feel like the one i hear about most often is Israel), but there are some prominent parliamentary-style assemblies (including the main national legislatures of the UK and Canada, i believe) that use a first-past-the-post district-based system. various hybrid systems are also quite common.

i would guess that proportionality does a lot more to promote party diversity than the details of parliamentary systems in general do, but Canda and the UK do seem to have stronger (or at least better represented in the national legislature) minor parties than we get here in the US.

i'd guess that the factor in these cases is that the parliamentary system allows minor parties that can build enough regional strength to get a few members in the house still have a chance at joining a coalition and influencing the choice of head-of-government, while the fact that the president is elected directly here means that even if you can get enough regional support to pull a few house seats, you're basically cut out from influencing the choice of executive, and will just end up being the hated spoiler party.