Complex sentence: Thảo began as a propagandist for various units of the army and for the secret Catholic Can Lao Party, whose system of informants and secret cells helped create the atmosphere of a police state and maintained the Ngo family's grip on power.
Split into simpler sentences: Thảo began as a propagandist for various units of the army and for the secret Catholic Can Lao Party. The Can Lao's system of informants and secret cells helped create the atmosphere of a police state and maintained the Ngo family's grip on power.