Many individuals and groups in Germany that were opposed to the Nazi regime engaged in active resistance, including attempts to remove Adolf Hitler from power by assassination or by overthrowing his established regime. German resistance was not recognized as a collective united resistance movement during the height of Nazi Germany, unlike the more coordinated efforts in other countries, such as Italy, Denmark, the Soviet Union, Poland, Greece, Yugoslavia, France, the Netherlands, Czechoslovakia and Norway. The German resistance consisted of small, isolated groups that were unable to mobilize widespread political opposition. Individual attacks on Nazi authority, sabotage, and the successful disclosure of information regarding Nazi armaments factories to the Allies, as by the Austrian resistance group led by Heinrich Maier prevailed alongside this as well. One strategy was to persuade leaders of the Wehrmacht to stage a coup against the regime; the 1944 assassination attempt against Hitler was intended to trigger such a coup. It has been estimated that during the course of World War II 800,000 Germans were arrested by the Gestapo for resistance activities. It has also been estimated that between 15,000 and 77,000 of those Germans were executed by the Nazis. These resistance members were usually tried, mostly in show trials, by Special Courts, courts-martial, People's Courts and the civil justice system. Many of these Germans had served in government, the military, or in civil positions, which enabled them to engage in subversion and conspiracy; in addition, the Canadian historian Peter Hoffmann counts unspecified "tens of thousands" in Nazi concentration camps who were either suspected of or actually engaged in opposition. By contrast, the German historian Hans Mommsen wrote that resistance in Germany was "resistance without the people" and that the number of those Germans engaged in resistance to the Nazi regime was very small. The resistance in Germany included German citizens of non-German ethnicity, such as members of the Polish minority who formed resistance groups like Olimp. Overview Historiographical debates on the subject on Widerstand have often featured intense arguments about the nature, extent and effectiveness of resistance in the Third Reich. In particular, debate has focused around what to define as Widerstand (resistance). The German opposition and resistance movements consisted of disparate political and ideological strands, which represented different classes of German society and seldom able to work together—indeed for much of the period there was little or no contact between the different strands of resistance.