No kind of representative government e.g. "democracy" or "republic" can work without ethnic, cultural, and religious unity.

The US has been fucked ever since giving blacks the vote, actually even before that, by allowing large numbers of Jews in to corrupt a society which was initially built by WASPs and based on English Law. Moving to a "secular" state concept, which was never envisioned by the Founders, ruined all hope. All the societies of Europe which have followed suit are fucked as well.

(one can also make an argument that even with homogeneity, the idea of universal suffrage is flawed and at the very least there should be a literacy test and a means test to avoid conflicts of interest - I think the history of the US shows clearly that letting women vote was a mistake)