Most political histories written to encompass the evolution of an idea tend to follow two paths: They focus on the idea as it develops in a single country or region, or they attempt to offer a comprehensive discussion of the idea as it evolves on an international scale. The first path often leads to over-specialization and obsession with miscellanea; the second path often results in shallowness and a lack of intellectual rigor.
David Priestland's book "The Red Flag" avoids both pitfalls. Priestland does an admirable job of tracing the lineage of the modern Communist movement. He begins with a discussion of the radical democratic ideals of the French Revolution, followed by a biographical sketch of Karl Marx and a discussion of Marx's key notions of labor, freedom, and alienation.
Priestland then breaks Marxism down into three main historical strains: the "Romantic"; the "Modernist"; and the "Radical." Priestland associates the Romantic strain with the early works of Marx, most notably "The Paris Manuscripts", the Modernist strain with Lenin and the early Bolsheviks, and the Radical strain with Mao and the Cultural Revolution in China. Priestland then proceeds to trace the development of these strands of Marxist thought as they developed according to the various social and political contexts of the various countries that claimed adherence to Marxian principles.
While it can be argued that this tripartite classification is somewhat arbitrary in its execution, I think the reader can excuse Priestland for such an undertaking. By adhering to this classification, Priestland is able to sort through the intimidating abundance of historical data and present it to the reader in a clear and intelligible way.
Finally, Priestland is to be congratulated for his dispassionate analysis of the international Communist movement. Too often such histories devolve into right-wing moral hackery of the crudest sort (e.g., anything written by Paul Johnson), or provide slavish excuses for the atrocities committed in the name of Marxism (e.g., Harpal Brar). Priestland is to be commended for both exposing the atrocities that occurred under various totalitarian regimes during the 20th Century, such as the USSR under Stalin and China under Mao, yet making it clear that such regimes should not be viewed as an "inevitable" outgrowth of Marxist thought. Priestland makes his case succinctly in this quote from the epilogue of "The Red Flag": "We do need to make moral judgments about historical crimes, but we also need to explain. Also, it is one thing to indulge a Brecht; another a Stalin or a Pol Pot." (p. 571)
In short, Priestland's book is comprehensive and well-written. Highly recommended.