Czechoslovakia, Yugoslavia, the USSR, Northern Ireland, Sudan, Iraq, India, Lebanon, Belgium, the United Kingdom. Etc. This is so obvious that I suspect you're trolling.
The rest of your comment is merely further demonstration that you are in denial of reality and elevate ideology over history and fact.
Pfffft, oh my God, really? lol. Are you seriously giving me such dumb examples?
Czechoslovakia, a nation that basically was a communist state most of it's life, then broke apart after the (surprise surprise) the USSR did.
Yugoslavia broke because of ethnic tensions, not multiculturalism. The culture was pretty much the same across the board for Yugoslavia, regardless of ethnicity, but it was ethnic tensions between the Slavs, the Bosnian and the Croatians that it ended up becoming a civil war.
Norther Ireland, really? Are you going to use this example and ignore Ireland's history, and the tension between Catholics and protestants? Again, has nothing to do with multiculturalism.
Sudan? Ethnic tensions, resource warfare, and a dominant cultural trying to force itself on other cultures through the use of violence. Not multiculturalism, but rather forced mono-culturalism.
Iraq? Is still technically united, but breaking because of the aftermath of the US-led Iraq war, and because a part of Kurdistan is also in Iraq. Not multiculturalism.
India? It's standing strong, and is going to get stronger. Like the US, India has different cultures from state to state, but they're united because of a shared sense of national identity.
Lebanon? United, has religious tensions, but the culture is pretty much mono-culture (Arab culture prevails, regardless of religious background). Not multiculturalism.
Belgium? It's still a rich nation, and nowhere near broken. I don't get why this was mentioned...unless you're trolling.
UK? Seriously? The UK was and still technically a nation that has colonies. It's not breaking because of multiculturalism, rather, it's because of it's colonial past. In fact, it's increasingly likely that the UK is here to stay, and Scotland will NOT split off from the UK, as independence is still not considered super popular among the general population.
I'm beginning to think you're a troll, nothing more. You wanna talk about history, how about you actually learn history because spouting nonsense.