Historical inquiry combines all of the disciplines of international studies. Politics, law, and foreign policy come under the purview of political history. In 2003, author Bill Bryson wrote a thin volume called A Short History of Nearly Everything. The historian's task is to garner all available relevant sources to construct a plausible story of the past. Historians can provide a long view of ideological debates in international affairs, such as the advantages and disadvantages of a global liberal economic system, the efficacy of spreading democracy in some regions of the world, and the influence of religion and nationalism on international conflict. Political agendas filter out dissonant historical evidence. Karl Marx devised a political-economic theory of history based on the "scientific" truth of class conflict. The history of religion and ideas provided the spiritual and philosophical foundations of temporal power. Historical accuracy played a secondary role to the narrative's didactic purpose.