He lived by fire and he died by fire. He was vile — coldblooded, amoral, ruthless. He was the man his time called for, and the man his time called forth — a vile time, by most standards. Its name is Sengoku Jidai, a period of prolonged civil war. Oda Nobunaga (1534-82) is its most representative character — a military genius and a moral monster.

He was a visionary, a shaper of the future, to which, if necessary — and it was — he would sacrifice the present.

Or was he simply power-mad?

The central government, long impotent, had collapsed altogether, leaving Japan a confused welter of domains ruled by ungovernable warlords — some 260 of them as of 1467. The Onin War that began that year dragged on for a decade, reducing Kyoto, the ancient capital, to a smoldering ruin.

The Zen poet Ikkyu (1394-1481) wrote: “One burst of flame and the capital — gilt palaces and how many mansions — turns before one’s eyes into wasteland.”

Physical wasteland breeds moral wasteland — a morality of the sword. “As the cherry among blossoms, so the warrior among men,” goes an old saying. No saint, the warrior. “The path of the soldier is a deceitful one,” wrote the Confucian scholar Kaibara Ekiken (1630-1714).

Bored with the peace of his own time, Ekiken looked back with nostalgia on Nobunaga’s era, perhaps on Nobunaga himself.

“Depending on the circumstances of the moment,” he wrote, “one might trick or betray one’s allies, usurp the spoils won by others or throw the land into turmoil and seize it from those above: As a matter of military tactics, there is nothing wrong with this. It is the way of warfare in Japan.”

The end of the Onin War brought not peace but fighting under different names, or under no names, for causes that defy attempts to make them sound noble.

Or, perhaps not. For beneath the sordid land hunger and lust for power, amid the carnage, the disdain for life, the shifting alliances and betrayals and breakdown of even a semblance of moral decency as anyone now living understands the term, an idea was taking shape, vague at first, clearer as time passed.

Nobunaga, with what mixture of idealism and cynicism it is impossible to know, was among the first to articulate it. His motto, tenka fubu (“the realm, ruled by might”) meant, in effect, national unification, under a ruler strong enough to quell chaos and impose order on fierce local lords.

He was the man and his the might, he thought. So it might have proved, had he lived.

He was born in 1534, son of a minor samurai in a minor province, Owari, roughly today’s Aichi Prefecture.

His father’s death in 1551 left the family headship in dispute, and the first act by which we know Nobunaga is his murder, by a foul stratagem, of a younger brother asserting rival claims.

The second is more significant — stunning, in fact. With 3,000 soldiers he crushed an army of 25,000 — probably the largest army in Japan at the time — led by a neighboring lord en route to Kyoto to press his own version of something like tenka fubu. If you’ve never heard of the Imagawa clan, it’s because Nobunaga effectively wiped it out — otherwise you might have.

He was suddenly much sought after as an ally. Alliances were customarily sealed with marriages. Nobunaga’s younger sister, Oichi, symbol to later times of the samurai woman quietly enduring the unendurable, around 1565 was given in marriage to a son of the Asai clan. In 1570, the Asai broke with Nobunaga and joined his enemy, the Asakura clan.

Didn’t they know who they were dealing with?

Defeated, a surviving Asai-Asakura remnant sought refuge in the Enryakuji, one of thousands of Buddhist temples on Mount Hiei overlooking Kyoto.

Buddhist monks then were not what they are now. They were armed and dangerous. Here was Nobunaga’s chance. His soldiers set fire to the surrounding dry fields. Thousands burned to death.

“Everything, everywhere,” says a contemporary chronicle, “from the central cathedral to the 21 shrines of the Mountain King, the bell tower and the library, were burned to the ground.”

Buddhism in Japan never recovered its dominating influence.

Oichi was permitted to return to her brother’s castle with her three daughters. Her infant son, however, was put to death.

By 1582, Nobunaga was master of Kyoto and of one-third of Japan. The nation’s future seemed his to mold. A resentful retainer turned on him, setting fire to the Kyoto temple in which he was hosting a tea party. Nobunaga’s body was never found.

The future was his anyway — or was it? It was, in that within 30 years of his death tenka fubu was no dream but reality, Japan firmly united under the rule of Nobunaga’s ally, Tokugawa Ieyasu, first of a long line of Tokugawa shoguns stretching all the way ahead to 1867.

In another sense, Nobunaga was less successful. Not he but his treacherous assassin was the hero of 18th-century kabuki re-enactments.

In one play, his killer declaims, “Heedless of remonstrance, Nobunaga destroyed shrines and temples, daily piling up atrocity upon atrocity. It was my calling to slay him for the sake of the warrior’s way, for the sake of the realm”

Never mind that in the Sengoku Jidai there was no “realm” — and not much of a “warrior’s way” either, unless it was the “way” articulated by Ekiken, or by a warlord named Uesugi Kenshin (1530-78), a Nobunaga rival and a Zen man who succinctly summed up both Zen and his times: “Those who cling to life die. Those who defy death live.”

Michael Hoffman’s latest book is “The Naked Ear” (2012).