Pat Buchanan and I take opposite sides on some issues, particularly with his emphasis on “culture wars” and his aversion to immigration. Nonetheless, I must give a qualified recommendation for his book Churchill, Hitler, and the Unnecessary War.
Tl;dr version: both World War I and II were unnecessary. The Brits won the war but lost their empire; they overextended, ran up debt to unsustainable levels. The conclusion of WW II effectively made the world safe for Communism.
The United States of America appears to be heading down a similar slope, made slippery with the blood of millions of victims in the Middle East; the military forces are overextended, and debt is at its highest level ever, $20+ trillion and rising.
For a longer perspective, I recommend The Rise and Decline of the State , by Israeli historian Martin Van Creveld.
In this book, Creveld argues that the nation-state originated as and is optimized primarily as an engine of conquest. Militaristic expansion is designed-in. The nation-state has been going out of fashion, largely for two reasons: conquest is uneconomic compared to international commerce, and nations now fear atomic weapons.
Conquest is at best zero-sum; whatever we take, you lose; a vicious cycle.
By contrast, when commerce is shorn of coercion, it tends to be positive-sum; when we exchange voluntarily, both benefit thereby; the world is that much better off when we trade. This is a virtuous cycle.