Spacecraft that re-enter from either orbital decay or controlled entry usually break up at altitudes between 84-72 km due to aerodynamic forces causing the allowable structural loads to be exceeded. The nominal breakup altitude for spacecraft is considered to be 78 km.
When spacecraft re-enter Earth's atmosphere, they often break up around altitudes of 84-72 kilometers due to the intense aerodynamic forces that exceed their structural limits.  The standard breakup altitude for these spacecraft is generally set at 78 kilometers.