External state of emergency (Article 115a ff GG)
The external state of emergency is present, if the federal territory is attacked with armed forces or if such an attack will be coming soon.
It is determined by the Bundestag with agreement of the Bundesrat upon the request of the Federal Government. (Article 115 a I GG).
Article 115 a I
Any determination that the federal territory is under attack by armed force or imminently threatened with such an attack (state of defense) shall be made by the Bundestag with the consent of the Bundesrat. Such determination shall be made on application of the Federal Government and shall require a two-thirds majority of the votes cast, which shall include at least a majority of the Members of the Bundestag.
If the Bundestag is prevented and if the situation requires immediate acting, then the Joint Committee takes the statement (Article 115 a II GG).
If the federal territory is attacked and if the responsible organs are prevented, then the case of defense is determined automatically with the beginning of the attack (Article 115a IV GG).
The command authority over the armed forces has now the Federal Chancellor (in peace the Minister of Defense) (Article 115 b GG).
Internal state of emergency (Article 35, 91 GG)
An internal state of emergency is for example a natural catastrophe or a revolution
Police forces, Federal Border Police and armed forces can be inserted in the Laender and landspreading.
Article 35 II
In order to maintain or restore public security or order, a Land in particularly serious cases may call upon personnel and facilities of the Federal Border Police to assist its police when without such assistance the police could not fulfill their responsibilities, or could do so only with great difficulty. In order to respond to a grave accident or a natural disaster, a Land may call for the assistance of police forces of other Länder or of personnel and facilities of other administrative authorities, of the Armed Forces, or of the Federal Border Police.