Centrist

Why does the United States have only 2 parties for government? I mean yes they have these (http://en.wikipedia.org/wiki/List_of_political_parties_in_the_United_States#Political_parties) different minorities; but only two major parties that are splitting the country apart by acting like children. I don't take sides really on matters of republican or democrat, I'm a centrist, therefore I see things what are more practical and what would work better, which could mean a little bit of republican ideas and a little bit of democrat ideas. In fact a lot of times I play devil's advocate just to have the other party to see the other side of the argument (Ha!). But back to my question, "why does the United States have only two parties for government?" I know of American political history on how these two parties became the major leaders in government, but why now still? There are so many other options to break their hold on monopolising our government the way they're doing. I even know of some republican and democrat (not personally, only from news) individuals that are NOT republican or democrat, but were elected to be so; so that they can be supported and get into office (too many sites, just look on google and wiki... though I know their sources are not too reliable many times). Hopefully someone will come on and answer this; or I might have to put this on the questions forum (hmmm....).
Anyways... I like to reiterate what I said, to complete my thought on the matter; for that  I mean on the comment "but why now still, there are so many other options to break their hold on monopolising our government the way they're doing." If the United States government had three or more parties, it would offset the balance of power, also there would not be such a deadlock as much as two parties would. The republicans and democrats split the nation so perfectly to distract the people of the real issues and keep a 'stale-mate tug-of-war' in Washington so nothing gets accomplished, made to look like nothing getting done, or simply drag everything out to blame party A so that party B can get into office (notice I not blaming either party, but both in a not so much of an indirect way).
So I would like anyone reading this post, first to think of what you really want out of your government then go to this 3rd party site http://www.politicalcompass.org/test and take the test (logically & honestly); it is long and a bit difficult if you don't know much about politics, economy, and so on , but it is well worth the time and learning to 'know thy self better.'
I took the test, hmmm, 9 times in my life time, first time I took it I was a republican, mostly from my parents' influence, 2nd time I took it, still a republican, 3rd time (a little over a year later) I found my self to be a democrat, 4th time (6 months later) a communist, 5th time the same, 6th time (a year after the 5th time) a centrist, 7th time the same, 8th time the same, and just recently (the day I wrote this post) after 2 years after the last time I took the test, making this the 9th time, I'm still in the middle near centrist but also leaning towards Social Libertarian/Authoritarian, which I find kind of funny, though they did change up the questions and how to answer them, used to you could click 'maybe,' which I pick a lot because it just depends on the circumstance to know how to answer some of those questions. But I can still accept the results, I'm still near the center, which I like to be, like I tell everyone, I like the middle-path, its hard to walk on sometimes, but I wouldn't have it any other way. Below is the image of where I stand (currently), the map is a good description of how people stand, and how close they stand next to, certain political views. Please try it yourself.