 Complete the following phrase:  OPEC often has difficulty agreeing on policy decisions because its member countries differ widely in their oil export capacities, production costs, reserves, geological features, population, economic development, budgetary situations, and political circumstances. Indeed, over the course of market cycles, oil reserves can themselves become a source of serious conflict, instability and imbalances, in what economists call the natural resource curse. A further complication is that religion-linked conflicts in the Middle East are recurring features of the geopolitical landscape for this oil-rich region. Internationally important conflicts in OPECs history have included the Six-Day War 1967, Yom Kippur War 1973, a 