The 107-country Outer Space Treaty signed in 1967 prohibits nuclear, biological, or chemical weapons from being placed in or used from Earth's orbit. What they didn't count on was the US Air Force's most simple weapon ever: a tungsten rod that could hit a city with the explosive power of an intercontinental ballistic missile.
Note that this treaty does not ban the placement of weapons in space in general, only nuclear weapons and WMD.!!
A kinetic bombardment or a kinetic orbital strike is the hypothetical act of attacking a planetary surface with an inert projectile, where the destructive force comes from the kinetic energy of the projectile impacting at very high velocities.