The Enemy Within by Larry Bond: Iranian Terrorist disguised as Neo-Nazi’s launch attacks all over America
Against All Enemies by Harold Coyle: Military VS Idaho Militia
Prayers For The Assassin by Robert Ferrigno: 2040. The USA is divided between Christian South and the Islamic Republic of America.
Darkest Days by Stan Gallon: Haven’t read it but sounds like it’s what you’re looking for.
The Third World War: August 1985 by Gen. Sir John Hackett: A future history written by a NATO commander during the Cold War postulating on what a conflict between NATO and the Warsaw Pact would look like.
The Untold Story: The Third World War by Gen. Sir John Hackett: Hackett’s follow up to the above
Team Yankee by Harold Coyle: Coyle takes Hackett’s WWIII scenario and writes about the experience of a group of American Tankers.
Dragonfire by Humphrey Hawksley: India goes to war with Pakistan and China. The USA, Europe and Japan back India, Russia backs China.
Breakdown by William W. Johnston: 2nd American Revolution
Defiance: An American Novel by Oliver Lange: Guerrilla resistance to a Soviet invasion
Clash of Eagles: A Novel of the Nazi Occupation of America: Alternate History. Guerrilla resistance to the Third Reich in the Eastern USA.
Arc Light by Eric L. Harry: WWIII and America getting nuked
America’s Last Days by Douglas Mackinnon: Coup d’état involving the military and FBI.
Invasion by Eric L. Harry: Chinese Invasion of America
Ian Slaters WWIII novels originally started as a Cold War scenario but he did a couple updates not that long ago dealing with modern scenarios. He also did the USA vs Militia series about a 2nd American Civil War.
Under Siege by Stephen Coonts: See’s Washington DC devastated by Narco-Terrorism
Jerry Aherns series The Survivalist
Red Army and The War After Armageddon by Ralph Peters
Almost any techno-thriller writer will get to this subject, check the biggies back catalogue (Clancy, Coonts, Dale Brown, Joe Weber ect.)
Their where also a bunch of pulp serial novels in the 80’s that dealt with similar scenarios (The Guardians by I forget, Tank War by Larry Steelbaugh, Countdown WWIII, End World, The Ashes ect)
Less mainstream dude named Mathew Bracken has a trilogy (Enemies Foreign and Domestic, Domestic Enemies: The Reconquesta, Foreign Enemies and Traitors) sound like their along the lines your looking for but fair warning I haven’t read them.
Molon Labe by the psyedonomous Boston T. Party
Unintended Consequences by John Ross
I’d also recommend Bruce Powe’s Killing Ground: The Canadian Civil War
Their was also a novel tie in for the video game Homefront and I believe a tie in for Tom Clancy's EndWar