Complex sentence: Although offering strong defences, the Flesquières position formed a dangerous salient in front of the British line, and when the Germans opened their spring offensive on 21 March 1918 one of their first objects was to pinch it out.
Split into simpler sentences: Although offering strong defences, the Flesquières position formed a dangerous salient in front of the British line. When the Germans opened their spring offensive on 21 March 1918, one of their first objects was to pinch it out.