LitCharts assigns a color and icon to each theme in The 5th Wave, which you can use to track the themes throughout the work.
Trust and Belief
Survival and Perseverance
Warfare and Dehumanization
Family
Summary
Analysis
The narrator, Cassiopeia “Cassie” Sullivan, talks about how human ideas about aliens (like flying saucers) are stupid. Those aliens are nothing like the Others, which is her term for the actual aliens who defeated humanity.
The first chapter establishes how the novel will attempt to treat an alien invasion with some degree of realism rather than as a fantasy. Although the novel contains fantastical events, it also comments on the real world, with humanity’s hypothetical reaction to an alien invasion in this novel drawing inspiration from how humans have responded to real events in the past.