who has given the concepts of ingroup and outgroup
Ingroups and outgroups The terminology was made popular by Henri Tajfel and colleagues during his work in formulating social identity theory. The significance of ingroup and outgroup categorization was identified using a method called the minimal group paradigm. Tajfel and colleagues found that people can form self-preferencing ingroups within a matter of minutes and that such groups can form even on the basis of seemingly trivial characteristics, such as preferences for certain paintings.[1][2][3][4][5]
Irreconcilables According to Stone's 1970 book, the Irreconcilables in the Senate fell into three loosely defined factions. One group was composed of isolationists and extreme nationalists who proclaimed that America must be the sole commander of its destiny, and that membership in any international organization that might have power over the United States was unacceptable. A second group, the "realists", rejected narrow isolationism in favor of limited cooperation among nations with similar interests. They thought the League of Nations would be too strong. A third group, the "idealists", called for a truly democratic league to foster peace and justice in the world. The three factions cooperated to help defeat the treaty. All of them denounced the League as a tool of Britain and its nefarious empire.