U.S. defense spending isn't excessive and, in fact, should continue to grow because it's both affordable and necessary in today's challenging world.

The United States spends a lot of money on defense—$607 billion in the current fiscal year. But Brookings national security scholar Michael O'Hanlon argues that is roughly the right amount given the overall size of the national economy and continuing U.S. responsibilities around the world. If anything, he says spending should increase modestly under the next president, remaining near 3 percent of gross domestic product.

Recommendations in this book differ from the president's budget plan in two key ways. First, the author sees a mismatch in the Pentagon's current plans between ends and means. The country needs to spend enough money to carry out its military missions and commitments. Second, O'Hanlon recommends dropping a plan to cut the size of the Army from the current 475,000 active-duty soldiers to 450,000.

The U.S. national defense budget is entirely affordable—relative to the size of the economy, relative to past levels of effort by this country in the national security domain, and relative, especially, to the costs of failing to uphold a stable international order. Even at a modestly higher price, it will be the best $650 billion bargain going, and a worthy investment in this country's security and its long-term national power.