I've seen this question before, asking to identify where the narrative takes place. It is World War II in Europe.
The references to "fighting the Germans when Poland had first been invaded" identify this narrative as happening during World War II in Europe. Other nations in Europe, notably Britain and France, had followed a policy of appeasement toward Adolph Hitler and Germany's efforts to add territory to its control. They allowed Germany to annex the Sudentland, and then did nothing when Germany took control of all of Czechoslovakia (in March, 1939). But when Germany invaded Poland in September, 1939, it was beyond clear that appeasing Hitler hadn't worked, and war was pursued. Germany's invasion of Poland was the beginning of World War II in Europe.
