After internal conflicts ravaged the former Yugoslavia during the 1990s, the UN and NATO intervened decided to turn Bosnia and Kosovo into protectorates devoid of sovereignty. The international organizations then declared their plans to turn both into multi-ethnic liberal democracies. Apparently, those who declared such goals must have forgotten that the ethnic groups in these areas have deep-seated hatred and/or mistrust for the other group(s) (as if the wars between the groups weren't enough evidence of this). Such an environment couldn't breed a stable dictatorship, let alone a democracy.
This fact is being borne out today, where all three ethnic groups in Bosnia are about to elect nationalist candidates in upcoming elections, showing no trust for candidates of other ethnicities, and in Kosovo, Serbs are planning to boycott the election due to the lack of security provided by the region's NATO-appointed rulers - the Albanian "Kosovo Liberation Army" who hates them.
If these examples, along with the ongoing "catastrophic success" in Iraq, aren't proof of the futility of international social engineering, then I don't know what is.