Why are ballistic missiles built with multiple stages?

Ballistic missiles are constructed with multiple stages primarily to increase their range and throw weight.1

The process of staging involves mounting rocket systems in a linear sequence. As the flight progresses, the missile sheds the mass of the spent stage—including its empty fuel tanks, pumps, flight controls, and associated hardware. By discarding this "dead weight," each successive stage has significantly less mass to accelerate. This design efficiency allows the missile to achieve higher velocities, travel farther, and carry a larger payload than would be possible with a single-stage vehicle.231

During the boost phase, these stages ignite sequentially to provide the precise propulsion required to place the missile on its intended ballistic trajectory. Once a stage exhausts its propellant, it drops off, allowing the next, smaller stage to take over and accelerate the remaining vehicle further. This technique is essential for overcoming the challenges of gravity and achieving the high speeds necessary for long-range flight.123