What is the main conflict in Starship Troopers by Robert A. Heinlein?

Starship Troopers tells the story of Juan Rico, a well-to-do youngster who joins the elite Mobile Army at the outbreak of the “Bug War”. He survives boot camp, rises rapidly through the enlisted ranks through heavy attrition, is culled off for Officer Training School, and survives his first experience as a platoon commander. Rico goes on to become a confident commander, passing to younger officers the wisdom he has absorbed from many mentors.