Complex sentence: The Post Office Department played an important intelligence role during World War I, enacting the Espionage and Trading with the Enemy Acts, monitoring foreign mail and acting as counter-espionage to help secure allied victory.
Split into simpler sentences: The Post Office Department played a role during World War I, enacting the Espionage and Trading with the Enemy Acts. Also monitoring foreign mail and acting as counter-espionage to help secure allied victory.