A nationalist country on the other hand has a government where the people, the culture and sometimes the religion/ethnicity of the country is put ahead of everything.
Nationalism just means anything pertaining to a nation, which is defined as a group of people who have something in common.
This doesn't even have to be a natural characteristic such as race, religion, or culture. It can be a made up characteristic called "National Identity" which essentially means that all people living in a country are part of that nation.
These ideas of nationhood can be radically different. For example, There is a whole left-right spectrum within nationalism.
Practically every single country in the post imperial era is also a nation. The dominant form of nationalism today is one that contrasts with said imperialism, that is that every person within a country should be treated equally, and that a government must be democratically chosen to be legitimate. There is nothing inherently bad about these ideas, and they do not entail supremacism, as you seem to be implying.
Socialism just means any idea that entails common ownership.
These ideas also vary wildly, from national socialsm (commonly referred to as nazism), to marxism-lenninism (commonly called "communism"), the mortal enemy of national socialism. One thing they all tend to share is being hostile towards christianity, which is why I don't like them.
There isn't anything conflicting in these ideas, as they are essentially completely separate ranges of ideas.
Edited 5/3/2016 21:49:14