Question

Which nations lost territory and which gained territory in Europe during or immediately after the Second World War? Some may have lost territory in one region and gained land in another.

lost territory:
gained new territory:

1. Czechoslovakia
2. Finland
3. Romania
4. Lithuania
5. Poland
6. Soviet Union

Answer 1

Below I list, for each country, the main territorial losses and gains in Europe that occurred during or immediately after the Second World War (c. 1939–1947). I note the principal regions and the key moments (1939–40 Soviet and Axis moves, the 1944–45 reconquests and Potsdam/Pary/1947 settlements). Some changes were restorations of pre‑1939 borders; others were permanent transfers.

1) Czechoslovakia
- Lost territory:
- Carpathian Ruthenia (Subcarpathian Rus') — annexed/absorbed into the Soviet Union (became part of the Ukrainian SSR) after 1944–46.
- (Temporary losses 1938–39: Sudetenland to Germany, southern Slovakia/Carpathian parts to Hungary — these were later reversed.)
- Gained new territory:
- No significant new permanent territory beyond restoration of the pre‑1938 borders (i.e., the Sudetenland was returned after 1945). The important permanent change was the loss of Carpathian Ruthenia.

2) Finland
- Lost territory:
- Large parts of Karelia (including the Karelian Isthmus and the city of Viipuri/Vyborg), parts of Salla, several islands in the Gulf of Finland, the Rybachy area/Petsamo (the latter ceded after the Continuation War/1944 armistice), and Finland also lost use of the Hanko naval base (leased 1940–41). These losses were fixed by the 1944 armistice and 1947 peace arrangements.
- Gained new territory:
- None — Finland was compensated politically in no significant territorial way in Europe.

3) Romania
- Lost territory:
- Bessarabia and Northern Bukovina — ceded to the Soviet Union in June 1940 and confirmed after the war (became parts of the Moldavian SSR and Ukrainian SSR).
- Southern Dobruja (Cadrilater) — ceded to Bulgaria in September 1940 (confirmed after the war).
- (Temporary: Northern Transylvania was ceded to Hungary in 1940 but was later reversed.)
- Gained new territory:
- Northern Transylvania — returned to Romania from Hungary in 1944–45 and confirmed in the post‑war settlements (so Romania regained this region).

4) Lithuania
- Lost territory / status:
- Lost its independence and was annexed into the Soviet Union (Lithuanian SSR) in 1940; after the German occupation and Soviet re‑occupation (1944–45), it remained part of the USSR — a loss of sovereign statehood.
- Gained new territory:
- As a Soviet republic, it came to include the Vilnius region (recovered/assigned in 1939–40) and the Klaipėda (Memel) region was brought under Lithuanian SSR control after 1945 (territorial arrangements tied to wartime and postwar settlements). (Overall, changes were largely the result of incorporation into the USSR, not independent Lithuanian acquisitions.)

5) Poland
- Lost territory:
- The eastern borderlands (the Kresy) east of the Curzon line — large areas including Lwów (Lviv), Wilno/Vilnius (the latter mostly went to Lithuania), and other eastern provinces — were transferred to the Soviet Union (incorporated into the Ukrainian and Belarusian SSRs).
- Gained new territory:
- Large western and northern territories taken from Germany (the "Recovered Territories"): most of Silesia, much of Pomerania, the former Free City of Danzig area, and parts of East Prussia (southern East Prussia) — these shifts were implemented after 1945 (Potsdam) and became the basis of postwar Poland’s borders.

6) Soviet Union
- Lost territory:
- No significant permanent territorial losses in Europe after WWII (temporary wartime occupations aside). The USSR did not cede European territory in the postwar settlements.
- Gained new territory:
- Baltic states (Estonia, Latvia, Lithuania) — incorporated in 1940 and re‑asserted after 1944–45, becoming Soviet republics.
- Eastern Polish territories (the Kresy) — annexed and incorporated into the Ukrainian and Belarusian SSRs.
- Bessarabia and Northern Bukovina — taken from Romania (forming part of the Moldavian SSR and Ukrainian SSR).
- Carpathian Ruthenia — taken from Czechoslovakia and incorporated into the Ukrainian SSR.
- Northern East Prussia (including Königsberg/Kaliningrad) — taken from Germany in 1945 and incorporated into the Russian SFSR.

Notes and caveats
- Many wartime changes (Munich/First and Second Vienna Awards, Soviet occupations of 1939–40) were reversed or modified after 1944–45; the lists above emphasize the permanent transfers recognized by the end of the war and by the Potsdam/Paris/1947 settlements.
- Some countries both lost and regained territory (e.g., Romania lost Bessarabia but regained Northern Transylvania; Czechoslovakia regained the Sudetenland but lost Carpathian Ruthenia).
- Borders were often adjusted at the village level in addition to the large transfers summarized above; I listed the major, widely recognized changes.