Wilson's War is similar in theme to Thomas Fleming's The Illusion of Victory (review) and reinforces many of its points. Like Fleming, Powell utterly rejects the notion that Wilson was a great President, holding instead that his bringing the U.S. into World War I had disastrous consequences. Indeed, Powell calls Wilson "the worst president in American history."
But of the two books, Fleming's is the stronger. Powell does give a broader historical focus, starting from the Napoleonic Wars and continuing through World War II. The coverage of the 19th century shows the nature of the European conflicts and hostilities that led to war in 1914. The discussion of the U.S. invasion of Mexico during Wilson's first term is also illuminating, helping to shatter the myth of Wilson as a wise peacemaker. But the continuation well past the ascent of Lenin and Hitler gives the impression of padding, doing very little for the book's stated thesis.
Powell regards U.S. intervention in the war as a decisive factor enabling the Nazis to take power in Germany and the Bolsheviks in Russia. The case he makes regarding Germany is very convincing. Without the decisive Allied victory, the concluding treaty wouldn't have imposed huge debts on Germany, spurring a nationalist movement of resentment, encouraging hyperinflation, and creating an atmosphere in which Hitler could thrive. Powell also shows that the moral case for supporting the Allies was weak, as was the national security justification.
In the case of Russia, Powell's case is interesting but less convincing. If the Kerensky government had managed to get out of the war, Lenin might not have been able to grab power. Powell repeatedly cites the loans which the U.S. made to Russia to keep it in the war, But he doesn't make a convincing case that the U.S.'s role was decisive. The pages which Powell devotes to the horrors of Stalin's regime are an important reminder of events which have been pushed somewhat into the background by Hitler's horrors, but they don't make the case for blaming Wilson any stronger.
Near the end, Powell briefly alludes to the breakup of the Ottoman Empire, with Britain and France grabbing large chunks of the Middle East. After the war Britain tried to set up an Iraqi government in the face of Sunni-Shiite conflicts; the problem remains unsolved today. I wish the author had devoted more of the book on the connections among Wilson, these events, and modern events rather than spending so much space on the USSR.
The story of American involvement in World War I and its disastrous consequences is an important reminder for our time, but Fleming presents it more convincingly. I'd recommend starting with Fleming and then perhaps reading Powell as a supplement.