North Korea, China, Russia, Uganda, etc. are examples of one party taking over; the USA is just a country that has one party (you don't seem to like) with most (but not all) of the political power at the moment.
China's history is more complicated, but is also the product of military conflict following colonial imposition by Japan. To suggest that either country's political system is the outcome of inherent structural weaknesses in multi-party democracy is absurd.
Please note that the comment I replied to has been substantially modified since I posted.