"Why can't we all get along?" Because people will have differences, and when your differences cannot be negotiated (or someone is a fucking psychopath), you start fighting.
Now throw in people who are different in a multitude of ways; skin color, language, culture, heritage, etc and mix them all together without one solidifying culture for everyone to reach, and you have the perfect mixture for war. And the worst part is, we have a fifth column in this country who will put competing groups at each others throats and have them fight; namely pitting all the PoC against the oppressive whites, and if the whites say anything, it's hate speech. People will always compete, especially with those different, but our problem is we have conspirators and agent provocateurs purposely stirring this pot to get us into another Civil War.