Complex sentence: The Axis forces achieved several tactical successes, which led to Auchinleck's decision to replace Cunningham with Major-General Neil Ritchie, but 8th Army relieved the siege of Tobruk and the Axis garrisons at Bardia and Sollum soon had to surrender.
Split into simpler sentences: The Axis forces achieved several tactical successes, which led to Auchinleck's decision to replace Cunningham with Major-General Neil Ritchie. The Eighth Army relieved the siege of Tobruk and the Axis garrisons at Bardia and Sollum soon had to surrender.