John Birmingham gained recognition in science fiction with his Axis of Time novels, in which a multinational naval force from the mid-21st century gets dropped into the middle of World War II, changing the balance of power and producing culture shock on both sides. In Without Warning, the start of a new series, the starting point is a different fantastic event: the sudden depopulation of most of North America by a mysterious energy field that causes spontaneous human combustion. The story tracks a handful of characters, mostly Americans, through the radically altered political landscape that results.

The Axis of Time books offered a somewhat handwaved explanation for its ‘castaways in time’ event in contrast to other recent ventures in the genre such as S. M. Stirling's Nantucket Island books or Eric Flint's Ring of Fire series. At the end of Without Warning, the key event is still unexplained. Birmingham's focus seems to be on a kind of double thought experiment: exploring what would happen to world politics without the United States, and exploring how the remaining fragments of the United States would reorganize.

The American armed forces logically are central to both questions. Birmingham's premise gives him a reason to write about military action and the culture of the military, subjects he obviously loves for their own sake. Without Warning can be read as a straightforward war story. But it can also be read as a story about the legal and constitutional relationship between the military and civil society—a question that has been with us at least since ancient Rome began appointing military dictators to hold emergency wartime powers.

Geopolitically, Birmingham's story can be read as a way of asking what the United States does for the rest of the world, and as a rejoinder to people who think the world would be better off without Americans. He shows the collapse of international order without an American presence: dictatorship in the United Kingdom, civil war in France between Muslims and fascists, nuclear war in the Middle East and the threat of it in South Asia. The huge American armed forces still in existence are no longer capable of playing a stabilizing role, without the United States as a logistic base and without clear command authority from a civilian government. Birmingham also addresses the collapse of the world's financial system, but not the threat of famine when American agricultural productivity is shut down—unless he's saving that for a sequel. This book can be read as a defense of the special role of the United States as an imperial peacekeeping power, comparable to Britain in the 19th century or Rome in the ancient world.

As to American internal politics, Birmingham focuses on a constitutional question: How can the supremacy of civil government over the military be preserved? A major conflict of the novel is between people who want to maintain as much of the Constitution as possible in a country made up of Alaska, Hawaii, and part of Washington, and people who want to put the armed forces in charge. This part of its story reaches its climax with a new constitutional convention. Here, I think, libertarian readers will feel that his heroes are clearly on the right side, favoring the rule of law over authoritarianism.

This is not a novel about a free society, or about a movement toward increased freedom. But it's certainly a cautionary tale, both about a world without American political influence, and about the potential for authoritarianism within American culture. And it's a very American novel, not least in its preoccupation with issues of legality even in the midst of chaos.