Floods of refugees followed many wars in the 20th century. For example, the wars in Indochina sent millions of Southeast Asians to Australia, Europe, and the United States.

The United States and France evacuated entire centuries-old island communities in the Pacific Ocean for nuclear testing, and Great Britain removed the entire population of Diego Garcia to create a military base there.

Millions of Russians moved through the Russian Empire and then the USSR during that nation's existence, leaving behind sizable Russian minorities. Many thousands more returned to Russia after the USSR's breakup.

I don't know, perhaps the mass expulsion of German civilians from the Eastern territories or the 1944-1949 Istrian exodus might qualify? While I'm in all honesty not particularly knowledgeable about the former - better wait for some other flaired user! - the other one saw almost 300,000 ethnic Italians leaving what where then Italy's North-Eastern territories (Istria and a few bits of Dalmatia) after these had fallen under Yugoslav occupation.

While the Slovene and Croat groups living in the area had indeed been oppressed (forced italianisation, beatings and, after 1941, concentration camps) by the Fascist regime, when both the government and the German occupators fell around 1943/44 they left a power vacuum that many exploited for own private retributions; around 5000 Italians were killed and their bodies uncerimoniously dumped into karst sinkholes commonly found in the area (foibe) or often thrown in there while still alive. This - as well as the partition of those territories between the Western Allies and Yugoslavians - prompted a mass exodus of people towards the more secure rest of the peninsula, with many just leaving all their possessions behind them (have a look at Trieste's Warehouse n° 18, where all the belongings which did not have a claimant anymore were stored).

It is worth noting that most of these victims were in reality innocent civilians; most of the Fascist perpetrators had already left around 1943, with the result that those people were either killed because of some form of private vengeance or for having been mistaken for Fascist collaborators.

Another instance of that could be that of the 20,000 descendants of Italian settlers from Libya who had to leave the country at the time of Muhammar Gheddafi's rise to power, in 1970. Recycling an old post of mine on the subject...

[...] After WW2, many returned home but some 44,000 chose to stay behind. However, on September 1st, 1969 all of this changed with Muhammad Gheddafi coming to power after having deposed the old King Idris. On July 21, 1970 all the assets of the Italian residents had, by force of a decree of the newly-established Libyan Revolutionary Command Council, been confiscated; the 'colonists' were ordered to leave with whatever they could carry on their persons while their land, shops, homes, furniture, cars were being requisitioned and their social security accounts frozen (as far as I know, no compensation was ever paid by the new Libyan government).

The last Italians had left the country on 7 October 1970; this date marked a national holiday - the "Day of Vengeance" - until 2011. Only in 2007 these people were allowed to visit the place they lived and grew up in.

• Look here, here, here and here for some photos of the exodus (indeed, all I could find).

• Here's a short video about their ordeal; unfortunately it's in Italian w/o subtitles.

The relationship between colonists and Libyans was not quite among the best, although much had been forgiven after the war (thanks at least in part to King Idris' tolerant stance). After 1969 most Libyan Jews left as well, and many of them settled in Rome.