Complex sentence: At the outbreak of the war it, like most other south coast piers, was deliberately cut in half to prevent enemy invaders using it; after the war it was in such a state of dereliction that it was completely demolished.
Split into simpler sentences: At the outbreak of the war it, like most other south coast piers, was deliberately cut in half to prevent use by enemy invaders. After the war the pier was in such a state of dereliction that it was completely demolished.