Simplify the following text for a Grade 9 native English-speaking person.
Original: In June 1941 , the European Axis launched an invasion of the Soviet Union , giving a start to the largest land theater of war in history , which , from this moment on , was tying down the major part of the Axis military power .
Simplified: In June 1941 , the Axis Powers invaded the Soviet Union , the largest theater of war in history . This invasion would harm the Axis military power greatly .