A boy holds a Polish national flag as people commemorate the Warsaw Uprising in Warsaw, Poland on Aug. 1, 2020. On Aug. 1, 1944, the Polish underground resistance, led by the Polish Home Army, began a major military operation to liberate Warsaw from Nazi occupation. The uprising, which lasted 63 days, was the largest military effort of any European resistance against Nazi Germany. (Photo by Jaap Arriens/Xinhua)

People gather to commemorate the Warsaw Uprising in Warsaw, Poland on Aug. 1, 2020. On Aug. 1, 1944, the Polish underground resistance, led by the Polish Home Army, began a major military operation to liberate Warsaw from Nazi occupation. The uprising, which lasted 63 days, was the largest military effort of any European resistance against Nazi Germany. (Photo by Jaap Arriens/Xinhua)

People gather to commemorate the Warsaw Uprising in Warsaw, Poland on Aug. 1, 2020. On Aug. 1, 1944, the Polish underground resistance, led by the Polish Home Army, began a major military operation to liberate Warsaw from Nazi occupation. The uprising, which lasted 63 days, was the largest military effort of any European resistance against Nazi Germany. (Photo by Jaap Arriens/Xinhua)

People gather to commemorate the Warsaw Uprising in Warsaw, Poland on Aug. 1, 2020. On Aug. 1, 1944, the Polish underground resistance, led by the Polish Home Army, began a major military operation to liberate Warsaw from Nazi occupation. The uprising, which lasted 63 days, was the largest military effort of any European resistance against Nazi Germany. (Photo by Jaap Arriens/Xinhua)