General:
Hark, A Vagrant
Thinkin' Lincoln
Frederick the Great
Times Like This
Untitled

Ancient:
When I Am King
Dawn of Time
SPQR Blues
Gastrophobia
The Cattle Raid of Cooley
Dingir Comic, Adventure of the Gods
Tales From the Middle Kingdom
The Brick Testament
Oghme
Odysseus the Rebel
Vikings' End
San: Three Kingdoms
Godseeker

Pre-18th century:
Get Medieval
Shi Long Pang
The Secret in the Cellar
Fortune's Fools
Much the Miller's Son
Rogues of Clwyd-Rhan
Machiavelli

The Enlightenment:
Family Man
Bite Me
The Dreamer
Loyalty and Liberty
The Paul Reveres
The Adventures of Brigadier General John Stark

19th century:
Goodbye Chains
High Moon
Crowfeathers
Dovecote Crest
The Guns of Shadow Valley
The Thrilling Adventures of Lovelace and Babbage
The Futurists
Ace of Diamonds
Ellie Connelly
Dracula
Byron Pinkleton
Sailor Twain
The Continentals

20th century:
Lackadaisy
Stalin VS. Hitler
Goldenbird
Bayou
The Night Owls
Femme-Noir Webcomics
She Died in Terrebonne
1977 (NSFW)
World of Hurt
Ulysses "Seen"
Kitty Hawk
Lovecraft is Missing
Chicago: 1968
Sam Hill
You Damn Kid
Sector 41

21st century:
A.D.: New Orleans After the Deluge
The Honduran Coup: A Graphic History
Shooting War
Get Your War On
Fishtown
For Real
Zahra's Paradise