Complex sentence: The 1st Far East Front would form the eastern half of the pincer movement, attack which would involve the 1st Red Banner Army, the 5th Army and the 10th Mechanized Corps striking towards Mudanjiang (or Mutanchiang).
Split into simpler sentences: The 1st Far East Front formed the eastern half of the pincer movement. The attack involved the 1st Red Banner Army, the 5th Army and the 10th Mechanized Corps striking towards Mudanjiang (or Mutanchiang).