A forced landing is a landing by an aircraft made under factors outside the pilot's control, such as the failure of engines, systems, components, or weather which makes continued flight impossible. For a full description of these, see article on emergency landing. However, the term also means a landing that has been forced by interception.
A plane may be compelled to land through the use, or threat of use, of force, if it strays off course into hostile foreign territory. The Chicago Convention on International Civil Aviation contains guidance in Annex 2 on "Signals for Use in the Event of Interception": customarily for the military plane approaches the airliner from below and to the left, where his plane is easily visible from the left seat where the captain sits. The intercepting plane waggles his wings to signal the demand to be followed.
Territorial airspace is under the sovereignty of the relevant state, and their domestic law would regulate the treatment of intruding aircraft. Consequences could include:
… aircraft that fail to identify themselves, enter the airspace without a necessary permission, deny to follow a prescribed route, head towards a prohibited zone, or violate […] a prohibition of flight may, by strict observance of the relevant standards and procedures, as a last resort, be intercepted, identified, escorted to the adequate route or out of the prohibited airspace, or forced to land by military aircraft of the territorial state.
... the international requirements for making an intruding plane follow an air-force escort to the ground – moving in front and to the left, where the civilian pilot can see the escort, and waggling the fighter's wings