The principle of "effective nationality" or the "genuine link" doctrine was laid down by the ICJ in the famous Nottebohm Case (Liechtenstein v.
Guatemala).
In this case, Mr.
Nottebohm, a German citizen living in Guatemala, obtained Liechtenstein nationality just before World War II.
After the war, Guatemala seized his property as an enemy alien.
Liechtenstein brought a case against Guatemala on his behalf.
The ICJ ruled that for a country to exercise diplomatic protection for a citizen, there must be a "genuine link" or "effective connection" between the individual and the state.
The Court found that Nottebohm's connection to Liechtenstein was not genuine, but merely a matter of convenience to change his status from a belligerent to a neutral national.
Thus, Liechtenstein could not exercise diplomatic protection for him.