Battle of Wilno
1939 CE.
Shown on the map at 54.667°, 25.317°.
The Battle of Wilno (modern Vilnius, Lithuania) was fought by the Polish Army against the Soviet invasion of Poland in 1939, which accompanied the German Invasion of Poland in accordance with Molotov–Ribbentrop Pact. On 18–19 September, Soviet forces took over the city of Wilno. Polish forces, concentrated in the west, were relatively weak in the east. The Polish commanders, unsure whether to actively oppose the Soviet entry into Poland, did not use the full defensive capabilities of the town and nearby fortifications, although the outcome of the battle would not have been likely any different, given the overwhelming Soviet numerical superiority.
Text from the Wikipedia article Battle of Wilno (1939), licensed CC BY-SA 4.0.