During the 1920s, Kelsen continued to promote his celebrated theory of the identity of law and state which made his efforts a counterpoint to the position of Carl Schmitt who advocated for the priority of the political concerns of the state. Kelsen was supported in his position by Adolf Merkl and Alfred Verdross, while opposition to his view was voiced by Erich Kaufman, Hermann Heller, and Rudolf Smend. An important part of Kelsen's main practical legacy is as the inventor of the modern European model of constitutional review. This was first introduced in both Austria and Czechoslovakia in 1920, and later in the Federal Republic of Germany, Italy, Spain, Portugal, as well as in many countries of Central and Eastern Europe.