Constructivism has become popular among academics by focusing on the role of ideas in world politics. Certainly ideas can powerfully mobilize people and justify actions. The construction and manipulation of ideas has always been part of the behavior and competition among leaders, nation-states and non-state actors. For instance, where borders are drawn is often socially constructed instead of following human and physical geography. Benedict Anderson’s Imagined Communities showed that nationalist persuasion can make people feel they are citizens of a country instead of their local region.
Many leaders use nationalism to whip up their citizens and increase their own power. The Roman Empire used the concept of citizenship for the foreign-born as glue to keep things together. Racism and colonialism were used to justify the European empires. The ideas of freedom and opportunity in America are a powerful magnet for immigrants. Human rights and environmental issues are championed by groups who bring change with very few resources, as in the international treaty against anti-personnel land mines, anti-whaling protests and campaigns against Feminine Genital Mutilation. The idea of democracy is part of what destroyed many dictatorships, including the USSR/Soviet Union.
All nation-states and groups develop ideologies to justify and explain their policies. And when ideas change, reality can change as well. For millennia, slavery was taken for granted. However, a group of committed anti-slavery activists used persuasion to make it socially unacceptable and ended slavery in Britain in 1833. So, let us acknowledge the power of ideas such as Marxism and Islam without drowning in postmodernist jargon such as, “material resources acquire meaning for human action only through the structure of shared knowledge in which they are embedded.” Constructivists say that ideas construct social reality. Realists would counter that nations and leaders USE ideas to construct social reality.