Where to now? What's their purpose? Just more surviving? No antagonists? And what's the deal with the black guy who keeps following the markings on the trees? So many questions....
Spoiler Warning
In the comic they don't find Eugene is lying until they are at the outskirts of DC. They are then approached by a guy named Aaron who is a "recruiter" for the Alexandria (main suburb of DC) Safe Zone. It is a few city blocks that are walled off. It is ran by a former US Senator named Douglas Monroe. Naturally after Woodbury the group is wary. Douglas is actually fairly competent. He assigns each person jobs. Rick becomes Town Constable. But he isn't supposed to carry his gun. He suspects a guy is beating his wife, when he finds out he beats the guy to death.
Rick transitions to leader (after Douglas's wife dies). He vows to reestablished Civilization at Alexandria.
Next big event a guy shows up at Alexandria who uses Karate to kill Walkers. His name is Paul Monroe (no relation to Douglas) but everyone calls him Jesus (because he looks like the stereotypical Jesus beard long hair etc). He is a recruiter for another community 17 miles away called Hilltop Colony. They start a friendly trading network. Hilltop has excellent farmland while Eugene (finally given something useful to do) has started large scale production of reloading bullets.
They then run across this biker gang called the Saviors. They aren't overtly religious but they revere their leader. His name is Negan and he is a big dude who uses the f word a lot. Think Patrick Warburton/Vinnie Jones. He carries a baseball bat wrapped in barbed wire as a weapon in which he names Lucille. He is a murderous psychopath but there is a weird "orderly" dictatorship about him. His group's base called the Sanctuary is an abandoned factory with Walkers chained to the fence to keep others out. He beats Glenn to death with said bat (because Ricks group killed a biker during the skirmish).
Negan's group basically serve as highway men. They will protect from Walkers but you have to submit to them. Give them half your supplies and such. He also has multiple wives.
Rick (and Hilltop) go to war with the Saviors. They are soon joined in this alliance by 3rd community that calls itself "The Kingdom". It is led by this crazy old African American guy who calls himself "King Ezekial" but they prove to be good allies. The Kingdom itself is ran out of an abandoned high school. In a weird nod to Zoochat, pre ZA he was a Zookeeper. The first thing said about Ezekial in the GN is 'Ezekial has a tiger". He has a bond with a female tiger named Shiva that protects him and lives off of eating Walkers (doesn't hurt her).
As I said Negan tries to take multiple wives. Over the course of this war, we meet his 2nd in command Dwight. Basically Daryl (who isn't in the GN). Angel Wing Leather Jacket vest, Redneck, Crossbow, the whole 9 yards. Negan screws up when he tries to take Holly (Dwight's wife) as his new wife. He and Dwight get into it and he burns Dwights face with a hot iron. Dwight was the one who killed Abraham in the first confrontation with Rick's group (by shooting an arrow through his eye).
Eventually Dwight becomes a triple agent on Rick's side but no knows his true loyalty. Before a big battle Negan orders the Saviors to dip their arrows/bullets/knives in Walker guts. That way any injury will infect you quickly. In the battle Dwight shoots Rick. It is later proven Dwight's loyalty to Rick in that Dwight didn't poison that particular crossbow bolt.
Rick's group wins the war eventually. He brings Negan down but then instead of killing him says he is going to make him serve as a prisoner. He then slits Negan's throat (he lives). They make peace with the remaining Saviors (with Dwight as Savior leader)
After the war is over there is a time jump of two years. Characters look different (Maggie is leader of Hilltop and has Glenn's son Hershel Jr.), a lot more horse riding, and they have a blacksmith so everyone carries Katana. The four communities have a trading network. Saviors keep the peace (as does Jesus). Rick is seen as the grand leader/messiah/great warrior celeb. Carl moves to Hilltop to be an apprentice Blacksmith.
Two highway men report to Rick that Walkers were talking to each other. Turns out they are the new threat. It isn't walkers but "Whisperers" people who wear Walker skin/clothes/mask to move among them. So far since the time jump we haven't seen Michonne or Dwight directly. Some think Michonne may have flipped out and is the Whisperer leader.