Complex sentence: The Latvian Army was disbanded under the occupation of the Soviet Union so when the Germans invaded in Operation Barbarossa in June 1941, Ādamsons is leading a partisan unit in Vidzeme which starts a skirmishes with retreating Red Army.
Split into simpler sentences: The Latvian Army was disbanded under the occupation of the Soviet Union. When the Germans invaded in Operation Barbarossa in June 1941, Ādamsons was leading a partisan unit in Vidzeme which was involved in skirmishes with retreating Red Army.