Complex sentence: Many writers of invasion-scare stories took as their starting point an assumed unpreparedness on the part of Britain's armed forces to counter the threat of invasion, and they wrote with the aim of raising public awareness of this deficiency.
Split into simpler sentences: Many writers of invasion-scare stories took as their starting point an assumed unpreparedness on the part of Britain's armed forces to counter the threat of invasion. They wrote with the aim of raising public awareness of this deficiency.