We have two major parties that are increasingly become two wings of the same party. Both have abandoned the American worker and embrace crony capitalism and protecting the rights of the corporate elites. When parties lose connection with the people they represent, other parties emerge, It is easier in parliamentary democracies to form parties that represent a greater diversity of views and have those views affect government.
In the US, there are definite, inherent advantages that favor a two party system. Yes, we have third parties but they are usually unable to impact our electoral system. And any third party with substantial support will morph into one of the two major parties like the Republicans did with the Whigs. And failing that, the ideas of a third party that gain traction with the public will likely be adopted by one or both of the major parties.
If the Reps fail to confront Obama on amnesty, I can see a third party forming around the protection of the rights of the American worker.
The UK arrived at a political consensus on reduced immigration under the slogan, "British jobs for British workers." It was started by the BNP and eventually adopted by the Tories, Labour, and the Liberal Democrats. But mere words did not solve the problem, hence the meteoric rise of UKIP, which its detractors like to label as far-right and racist. In fact, recent polls asking the question, "Which party best supports the British worker?", UKIP got the most votes even more than Labour.
This May we may see an historic change in British politics. UKIP could very well become a "major" political party replacing, more than likely, the Liberal Democrats. The main issues will be immigration and the related issue of staying in the EU. Some may consider UKIP to be Nazis, but the reality is that the immigration issue is changing the electoral landscape throughout Europe. And I see the same thing happening in the US.
Brits are pretty much a two party system, though not for the same reasons we are. So if a UKIP rises, it will likely come out of the conservatives membership. They would still be a two-party system, unlike France or Germany in 1928-32, or many other Euro countries, where (and I keep saying this) parties LIKE the 1932 Nazis or the 1980s Green in Germany can get power they otherwise would never get.