Complex sentence: Once he has a cadre of Lensmen available to defend civilization, Samms uses them to begin tracing leads to the major threats to civilization, crooked politics, drugs, and pirates attacking merchant ships in space.
Split into simpler sentences: Once he has a cadre of Lensmen available to defend civilization, Samms uses them to begin tracing leads to the major threats to civilization. Crooked politics, illegal drugs, and pirates attacking merchant ships in space.