The break up of the Habsburg, Ottoman and Russian Empires at the end of the First World War was a tragedy. The Habsburg Empire united all the intrermingled nationalities in the Danube Basin into one federation bound together by loyalty to one monarch at Vienna, one religion (Catholicism) and using one lingua franca (German). They all had equal rights In 1918, it was carved up into supposedly homogeneous nation states. In actual fact those states all contained large ethnic minorities, who were henceforth discriminated against as non-nationals. Sigmund Freud was appalled, and condemned the architect of this scheme in his book Woodrow Wilson: A Psychological Study. Ironically, Wilson was President of a multi-ethnic country. Worse was to follow. During the Second World War, the Jewish minorities were exterminated, and afterwards, many other national minorities, who had likewise lived peacefully under benign Habsburg rule for centuries, were forcibly expelled, eg Germans in Hungary, Italians in Slovenia, Serbs in Croatia, Sudeten Germans in Czechy, and so on. A quarter of a million people thereafter in the 1990s perished in ethnic massacres in Bosnia.
A similar story unfolded in the Ottoman Empire. It had a history of tolerance; Jews were invited to settle there after being expelled from Spain in 1492. It had a civil service based on talent, and many of its leading citizens (including Sinan the Architect) were ethnic Greeks. Every town had four quarters: Armenian, Jewish, Muslim and Orthodox (as the Old City Of Jerusalem still does). They all lived together in peaceful co-existence under the overlordship of the Sultan at Istanbul. All that was required of them was paying taxes, which by present standards were very low. Since the Empire’s demise and its partition into rival states by the Treaty of Sevres in 1920, atrocity after atrocity has ensued, eg depatriation of Palestinians, civil war and massacres in Jordan, Lebanon and Syria, violent revolutions in Iraq and Yemen etc
In the multi-ethnic Russian Empire, the break up was tempered by the reincorporation of most of its territory into the Soviet Union in 1922. The latter’s implosion in 1991 meant the end of the Pax Sovietica and heralded chaos, ie wars between Armenia and Azerbaijan, between Russia and Georgia, massacres in Chechenya, violent revolutions in and invasions of Ukraine, emigration of ethnic Russians and so on.
The break up of the British Empire and end of the Pax Britannica was a similar tale, eg ethnic civil wars in Nigeria, Pakistan, Sri Lanka and Sudan, violent partition in Cyprus, Ireland and India, and repressive dictatorships.
The Twentieth Century produced the pernicious doctrine of nationalism based on the false premise that people of different ethnicities cannot or will not live together in peaceful co-existence. Multi-ethnic states, therefore, had to be forcibly destroyed and replaced by smaller racist nation states. There is, however, a glimmer of hope emerging. The European Union, the Eurasian Customs Union and free trade and currency unions in Africa are resurrecting the civilising concept of multi-ethnicity.