Complex sentence: This portrayed them as fanatic and ruthless with a desire for overseas conquest without seeing the consequences and this was reinforced when the Japanese attacked Pearl Harbour in 1941 and many studios first impulse was to capitalise on the theme of treachery and brutality.
Split into simpler sentences: This portrayed them as fanatic without seeing the consequences and ruthless with a desire for overseas conquest. This was reinforced when the Japanese attacked Pearl Harbour in 1941 and many studios first impulse was to capitalise on the theme of treachery and brutality.