EUROPE agreed to massive annexations of territory and population transfers

At the end of World War Two, the victorious Soviet Union, a Communist --that is, "Leftist"-- state, by the way, carried out massive transfers of territory from Germany to Poland and the USSR itself, from Czechoslovakia to the USSR, from Roumania to the USSR, from Poland to the USSR, and from Finland to the USSR. Further, mass transfers of civilian population were carried out in these annexed or transferred territories. About 15 million Germans and ethnic Germans were transferred to the rump of Germany, some three million ethnic Germans being expelled from the "Sudetenland" region retaken by Czechoslovakia after serving as one of Hitler's political goals before the war. A few million Poles were transferred from western Belarus and Ukraine that were transferred from Poland to the USSR. They were resettled in the new western areas of Poland annexed from Germany. About 400,000 Finns were transferred too. The city of Fiume in Italy was annexed to Yugoslavia, and the city's name changed to Rijeka. Tens of thousands of Italians were expelled, driven out. Some were massacred by Yugoslav Communist partisans.

The USSR and the other countries carrying out population transfers were Communist-"Leftist" states. But Roosevelt and Churchill had basically agreed to this policy at the Yalta conference in February 1945.

Curiously, when Israel might be the beneficiary of resettling the Arab refugees from 1948, then the Western powers all of a sudden sprout humanitarian principles. The Arab 1948 refugees must be kept in camps funded with Western money (mostly USA $$) until a political settlement with Israel, all the while these refugees and their descendants being used as a moralistic political reproach against Israel.
Nevertheless, the territorial changes in Europe after WW 2 were accepted by the European states at the Helsinki Conference of 1975. All European states but Albania were represented at the conference.

The Helsinki Agreement, Final Act, 1975, also called the Declaration of Principles Guiding Relations between Participating States, declares:

Clause 4 - "The participating states will respect the territorial integrity of each of the participating states. Accordingly, they will refrain from any action. . . against the territorial integrity, political independence, or the unity of any participating state."

This means that 35 European states committed themselves to respecting the border and territorial changes made in Europe at the end of the War which had displaced or "transferred" millions of Europeans. But in the Middle East they have other principles.