Czechoslovakia or Hungary keeps Carpathian Ruthenia. I honestly doubt it would drastically change anything for the USSR.
(I just realized the title says YOUR country. My apologies)
Makes the intervention in Hungary and Czechoslovakia more difficult, plus significant effects on the internal politics of Slovakia (Hungary was never going to retain territory given to them by the Nazis).
If this has to be a post-1900 POD, have some version of the Hoare-Laval Pact go through during the Second Italo-Ethiopian War where Ethiopia becomes an Italian client state with a Fascist government in Addis Ababa whole having most of Ethiopia’s Tigrayan and Somali-inhabited regions go to the Italians. History largely goes the same as IOTL except this Fascist Ethiopia takes the chance to reclaim the territories it lost to the Italians in 1935-36 and some more during World War 2. Ethiopia takes the chance to annex Italian Eritrea and French Somaliland during the war while reclaiming what parts of the Ogaden were lost.
Ethiopia with Djibouti would have a sea access even if Eritrea is lost, which would be a very significant change. Plus even worse conflicts with Somalia.
Finland manage to take East Karelia and Kola during Russian Civil War. This causes some changes but it is pretty hard change borders and not change anything.
Russia being cut off from its only ice free port on the Arctic Ocean is an enormous change. This seems to be the opposite of the challenge - change the most by taking as little territory as possible.
More decisive political leadership, means that Greece can easily get Cyprus, and without any bloodshed whatsoever. Had Greece entered the Great War on the Entente side earlier, the British had promised us Cyprus, and had Greek governments in the early 1950s been more cooperative with Britain and the US, Cyprus would have been Greek. That said, it might have led to a full Greco-Turkish War come the Colonels' Junta(if that ever happened), so I don't know whether it would be a good idea.
Would have a huge effect on Greek-Turkish relations. No division of Cyprus is also very significant, even from a broader point of view (the question of unrecognized states, the balance of force in the Eastern Mediterranean, the exploitation of gas fields around Cyprus and so on.
The referendum in Malta decides that the Island Will join Italy instead of the UK or going indipendent.
There was no such referendum. And Italy possessing Malta would be significant due to the strategic importance of the islands.
belgium gets luxembourg(part of netherlands at the time), dutch limburg, zeeland(flemish) at the independence and somehow gains french flanders from france later(lille)
All of these are pretty unlikely. Also all of these annexations would change substantially the ethnic balance in Belgium. All of these would significantly change the relations between Belgium and its neighbors.
also more reparations in ww2 gets us Aachen/koln (assuming belgium has dutch limburg already bordering the region)
Cologne is a major city with a wholly German population. For a country the size of Belgium this is not only a significant change, it basically changes the whole country.
The Allies decide 1944 that the german eastern border lay on the Eastern Neisse and not on the Lusatian Neisse.
This is a question of the expulsion of nearly three million people and whether Poland contains their fourth largest city. How is that nothing.