Complex sentence: In the south, the First Panzer Army's advance on Grozny stalled after meeting heavy resistance on the ground from Soviet forces supported by the 14th Air Army, which blunted their attacks.
Split into simpler sentences: In the south, the First Panzer Army's advance on Grozny stalled. It met heavy resistance on the ground, from Soviet forces supported by the 14th Air Army, which blunted their attacks.