What caused the late heavy bombardment?

The Late Heavy Bombardment (LHB), occurring around 4.1 to 3.8 billion years ago, is thought to have been caused by gravitational perturbations in the outer solar system, particularly involving the migration of the giant planets—Jupiter, Saturn, Uranus, and Neptune. This migration likely destabilized the orbits of smaller bodies in the Kuiper Belt and the asteroid belt, sending a significant number of these objects toward the inner solar system. The resulting influx of these impactors led to the intense period of bombardment observed on the Moon and other celestial bodies.