Comment Why only two parties? (Score 1) 235
A standard "poly sci" answer would be that it is not that majority and minority parties took over everything in the rules of the US Congress - the phenomenon derives from the nature of the US electoral system.
When you elect a single candidate from a territory (a President from the nation as a whole, a Senator from a state, etc.), this creates a very powerful incentive for all people in the system to reduce the relevent choices down to two. Suppose you have three parties contesting elections of this sort. As a quick and dirty principle, we will also suppose that everyone can rank all three parties in terms of preference, and that those rankings are reasonably consistent - supporters of party A will tend to rank all three parties in the same order (which, since we are being generic here, we can describe as A,B,C - meaning A is their first choice, and C is their last choice) and supporters of the furthest opponent (party C) will tend to rank the parties in the opposite way. If all three parties keep contesting elections, there will almost certainly be many cases where two of the parties realize that if they worked together, they could defeat the remaining party which is currently winning the election - and they would be happier with the result. For example, party A gets 40% of the vote, party B gets 35%, and party C gets 25% - so parties B and C realize that if they united behind the candidate from party B, they would win the election, and they would prefer that result. The same logic affects voters (who don't want to "waste" their vote), party organizers (who want to win elections for their party), issue activists (who want to get their preferred policies adopted), etc. Of course, once the vast majority of elections are being contested between two parties, it is quite likely that rules in the Congress will reflect that partisan "fact of life."
This contrasts sharply with the experience of many European countries, which use a proportional representation system of elections. They do not divide territory up into single-member districts, but instead cast votes nationwide, and allocate seats within the legislature in proportion to the votes received (ignoring a broad range of variation in mechanics - there are a whole bunch of different proportional representation schemes). In these countries, we usually see a noticeably larger array of different parties regularly participating in elections, and we see entirely different forms of legislative organization as well.
Of course, this explanation still has a few holes. The continued survival of the British Liberal party, and the rise of the Social Democrats in Britain, and the New Democrats in Canada are still seen as anomolies (both Britain and Canada use single-member district elections). There are probably additional "problem" cases elsewhere in the world (my comparative politics classes were taken several years ago.) However, I think it is fair to say that for many political scientists, the interesting question is not why there are only two parties in the US, but why there are more than two in Canada and Britain.
When you elect a single candidate from a territory (a President from the nation as a whole, a Senator from a state, etc.), this creates a very powerful incentive for all people in the system to reduce the relevent choices down to two. Suppose you have three parties contesting elections of this sort. As a quick and dirty principle, we will also suppose that everyone can rank all three parties in terms of preference, and that those rankings are reasonably consistent - supporters of party A will tend to rank all three parties in the same order (which, since we are being generic here, we can describe as A,B,C - meaning A is their first choice, and C is their last choice) and supporters of the furthest opponent (party C) will tend to rank the parties in the opposite way. If all three parties keep contesting elections, there will almost certainly be many cases where two of the parties realize that if they worked together, they could defeat the remaining party which is currently winning the election - and they would be happier with the result. For example, party A gets 40% of the vote, party B gets 35%, and party C gets 25% - so parties B and C realize that if they united behind the candidate from party B, they would win the election, and they would prefer that result. The same logic affects voters (who don't want to "waste" their vote), party organizers (who want to win elections for their party), issue activists (who want to get their preferred policies adopted), etc. Of course, once the vast majority of elections are being contested between two parties, it is quite likely that rules in the Congress will reflect that partisan "fact of life."
This contrasts sharply with the experience of many European countries, which use a proportional representation system of elections. They do not divide territory up into single-member districts, but instead cast votes nationwide, and allocate seats within the legislature in proportion to the votes received (ignoring a broad range of variation in mechanics - there are a whole bunch of different proportional representation schemes). In these countries, we usually see a noticeably larger array of different parties regularly participating in elections, and we see entirely different forms of legislative organization as well.
Of course, this explanation still has a few holes. The continued survival of the British Liberal party, and the rise of the Social Democrats in Britain, and the New Democrats in Canada are still seen as anomolies (both Britain and Canada use single-member district elections). There are probably additional "problem" cases elsewhere in the world (my comparative politics classes were taken several years ago.) However, I think it is fair to say that for many political scientists, the interesting question is not why there are only two parties in the US, but why there are more than two in Canada and Britain.
