The main one in Europe was of course the Eastern Front, where the Red Army was on the offensive and was winding up for their major offensive, Operation Bagration. Soviet forces had recently entered Romania and were approaching their pre-war borders with Poland and the Baltic states.

On the Italian Front, Monte Cassino had finally been taken on May 18th and the Allies liberated Rome two days before D-Day.

The Continuation War between Finland (now with heavy German assistance) and the USSR was also ongoing and the Red Army would open their last major offensive of this war on the day after D-Day.

In Yugoslavia, things were going badly for the Germans and the Yugoslav partisans under Tito were looking to liberate their country and push the Germans and Bulgarians out entirely.

In the China-Burma-India Theatre, British and commonwealth forces were undergoing a major Japanese offensive (Operation U-Go) and holding out at Imphal and Kohima on the Burmese-Indian border awaiting relief. Meanwhile in China, the Japanese Ichi-Go offensive was underway against Nationalist Chinese forces, who were having the worst of it.

In the Pacific Theatre, the US and Australian forces were still fighting in New Guinea and on the day before D-Day, the B-29 Superfortress flew its first mission, bombing Bangkok. Shortly after D-Day, B-29s based in India bombed Japan for the first time. US strategy in the second half of the year would be geared around securing islands where air bases could be built within B-29 range of Japan, such as Saipan.