1634: The Baltic War by Eric Flint and David Weber

After a cosmic accident sets the modern West Virginia town of Grantsville down in war-torn seventeenth century Europe, the United States of Europe is forged in the fire of battle.  The Baltic War reaches a climax as France, Spain, England, and Denmark besiege the U.S.E. in the Prussian stronghold of Lubeck.  The invention of ironclads, the introduction of special force tactics during a spectacular rescue operation at the Tower of London – the up-timers plan to use every trick in the time traveler's book to avoid a defeat that will send Europe back to a new Dark Age! 
Multiple New York Times best-seller and creator of the legendary "Honorverse" series David Weber teams with New York Times best-selling alternate history master Eric Flint to tell the tale of the little town that remade a continent and rang in freedom for a battle-ravaged land in the latest blockbuster addition to Flint's "Grantsville" saga!

"This is a thoughtful and exciting look at just how powerful are the ideals we sometimes take for granted, and is highly recommended[.]"
— Publishers Weekly on Flint and Weber's 1633.
"[R]eads like a Tom Clancy techno-thriller set in the age of the Medicis…"
— Publishers Weekly on New York Times best-seller, 1634:  The Galileo Affair.