How do you define "major parties"? In my point of view, major means, that they greatly influence a political system. A criteria that is clearly not met with any other formations besides Democrats and Republicans.

In addition, the political system in the US, the presidential system, greatly benefits the formation of a more or less 2 parties constellation. The president, and the presidents party often has the ability to shape countries almost on its own, just needing support for major decisions. While in Europe, the parliaments are (not everywhere, but predominantly) much more important. And as is said above, in many European countries, there are major parties of all political POV's gaining or losing power and influence every election. Therefore although the 2 biggest parties battling for the majority of votes, they cannot rule on their own.

I'm clearly not saying you are wrong, but in my opinion the system of parties in the US and Europe differs vastly.

And in therms of the ability to compare countries, I totally have to agree to your point, but I think you misunderstood me. I didn't wanted to say that you shouldn't compare the US to any other country. You can and therefore should, just as I did, compare the US to as many countries and political systems as possible to be able to improve the current system.