Harry Turtledove

"It's 1974, and Jerry Stieglitz is a grad student in marine biology at UCLA with a side gig selling short stories to science fiction magazines, just weeks away from marrying his longtime fiancée. Then his life is upended by grim-faced men from three-letter agencies who want him to join a top-secret "Project Azorian" in the middle of the north Pacific Ocean-and they really don't take "no" for an answer. Further, they're offering enough money to solve...

An alternate-history novel in which, after winning the Civil War, the Confederate States of America are attacked by the United States for buying parts of Mexico. The novel centers on ex-Civil War protagonists, including an Abraham Lincoln who has embraced socialism. By the author of Guns of the South.

An alternate history in which the course of the Civil War is changed by the arrival of a man from the year 2013 who offers to supply General Lee and the Confederacy with AK-47 rifles.

On December 7, 1941, the Japanese launched an attack against United States naval forces stationed in Pearl Harbor, Hawaii. But what if the Japanese followed up their air assault with an invasion and occupation of Hawaii? With American military forces subjugated and civilians living in fear of their conquerors, there is no one to stop the Japanese from using the islands' resources to launch an offensive against America's western coast.

From the New York Times–bestselling “standard-bearer for alternate history”: A spy takes on the enemies of the Byzantine Empire (USA Today).
In another, very different timeline—one in which Mohammed embraced Christianity and Islam never came to be—the Byzantine Empire still flourishes in the fourteenth century, and wondrous technologies are emerging earlier than they did in our own.
Having...

Book 1 of a World War II alternative history trilogy. A three-decades-old peace has held in North America as Japan dominates the Pacific, the Russian Tsar rules Alaska, and England under Winston Churchill, chafes for a return to glory. But, behind the facade of world order, America's a bomb waiting to go off. Jake Featherston, president of the Confederacy, sends his planes to bomb Philadelphia, and Gen. George Patton's armored divisions cut America...

Beginning with Into the Darkness, Darkness Descending, and Through the Darkness, bestselling author Harry Turtledove ("The master of alternative history"-Publishers Weekly) has been telling an epic tale: the story of a world war, comparable to the terrible world wars of our own 20th century, in a world where magic works.
Imagine the drama and terror of the Second World War-only the bullets are beams of magical fire,

...

"The second entry in the alternate-world 1950s series finds General MacArthur igniting a nuclear war that nearly destroys the planet, placing once-untouched survivors in the middle of an escalating showdown between Russia and the U.S."--

"What would happen if the ancient prophecy of the End of Days came true? It is certainly the last thing Eric Katz--a secular archeologist from Los Angeles--expects to discover during what should be a routine dig in Jerusalem. But perhaps higher forces have something else in mind. For when a sign presaging the rising of the Third Temple is located in America and a dirty bomb is detonated in downtown Tel Aviv, events conspire to place a team of archaeologists...

Neville Chamberlain, instead of appeasing Hitler, stands up to him--as alliances are re-examined and reworked and a Japanese attack on American territories draws the U.S. into the war.