Despite massive worldwide growth of government in the twentieth century, there have been periods in the U.S. and other countries when growth has slowed or reversed. Government growth is not inevitable. Explanations of government growth fall into three major categories. Path-dependent theories emphasize factors that continually push the size of government up, so the current size is in part a function of its past size. Theories about the equilibrium size of government explain why government is big, but not why government grows. If equilibrium conditions change, that can produce government growth. Theories also describe ideological shifts that cause people to want, or at least accept, bigger governments. All these explanations could have an effect on government growth. However, none appears to be persuasive enough to explain all the growth that occurred.