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
Cassie has now been traveling for three days. She sees useless cars in clumps, like a dead pack of animals, but she likes how they provide cover for her. She can smell the fires coming from Cincinnati before she even sees the city. As she approaches, she stumbles onto some dead bodies.
Cars used to be a sign of humanity’s technological prowess, but now they just serve as a reminder of how fragile humanity’s control over the earth was. Still, Cassie finds use for the cars (as cover) even after they’ve outlived their intended use, showing how the apocalypse makes people resourceful.