War on Two Fronts

 is the 1st chapter of the 19th volume and the 75th chapter overall of the Attack on Titan manga, written and illustrated by Hajime Isayama.

Overview
As the Beast Titan and his forces begin their attack, the Survey Corps finds itself trapped atop Wall Maria with no way to retreat. Amid the chaos, it is revealed that Reiner and Bertolt may not be the only intelligent Titans among the Beast Titan's army, and the Corps is backed into a corner by the Beast Titan's attack strategy. While Reiner targets the Corps' horses in an attempt to take away their only means of retreat, Erwin devises a plan to save the Corps from the Beast Titan's strategy by using Eren as bait to force their enemies to choose: pursue and attempt to capture Eren, or risk losing their only chance to kidnap him in favor of massacring the Survey Corps. Taking the bait, Reiner pursues Eren, and the two engage each other in the middle of Shiganshina District. As Eren releases all of his frustrations upon Reiner, the soldiers of the Survey Corps prepare to join in the battle with their new and improved weapons.

Summary
As the Beast Titan and his army advance, Erwin watches them, wondering who will win the battle: the Titans, or the human race. As Levi informs Erwin that Reiner is approaching them, Reiner places a glowing hand on his shoulder before charging toward the Wall. As Reiner begins scaling the Wall, Erwin instructs the Survey Corps to stay away from Reiner and avoid engaging him.

As Hange's squad looks on, Eren requests to know why Erwin hasn't issued an order to attack. Hange explains that he is likely still watching their enemy's moves.

As Erwin continues to observe the Beast Titan's forces, he notices a peculiar sight: a Titan crawling on all fours behind the Beast Titan, with supplies strapped to its back. Deducing that the Quadrupedal Titan is not one of the Titans that just transformed, Erwin hypothesizes that it may be a scout for the enemy, and that it may have been the one that alerted Reiner to the Corps' presence. Erwin informs the soldiers that the Quadrupedal Titan is intelligent, and suggests to them that there may be even more like it present.

Erwin's deductions are interrupted by the Beast Titan who, to everyone's surprise, commands the Titans to advance by smashing his fist into the ground. As he watches the 2-and-3 meter class Titans advance, Erwin realizes that the Beast Titan intends to use the same strategy employed at Castle Utgard: he will cut off the Corps' only means of escape by attacking their horses first. Erwin realizes that, if successful, the Beast Titan will not only cut off the Corps' escape path, but will also cut off their supply route. With no escape path, and no supplies, the Titans would simply be able to wait until the members of the Corps are too weak from hunger, and then simply snatch Eren from them.

Armin reminds Erwin that the Corps still hasn't been able to find Bertolt, but Erwin is more concerned with whether the Corps should allow the Titans to kill their horses. After some thought, Erwin instructs Squad Dirk and Squad Marlene to meet up with Squad Klaus and protect the Corps' horses, while Squad Levi and Squad Hange fight the Armored Titan with their new weapon, the Thunder Spears.

As the Squads deploy, Erwin stops Levi and informs him that he won't be accompanying his Squad in defending Eren, and will instead help protect the horses and, if possible, kill the Beast Titan. Levi agrees, promising Erwin that he will atone for his inability to kill Reiner by killing the Beast Titan. As Levi departs, Erwin speaks to Armin, and informs him that he and Hange are the two that he wants to entrust the Corps' forces to.

As he reaches the top of the Wall, Reiner surveys the battlefield, as the Survey Corps begins to engage the Titans. Reiner thinks about his mission, assuring himself that killing the Corps' horses will be enough, and that no matter how skilled Levi may be in battle, he is nothing compared to the Beast Titan.

As Levi's blade is dislodged from the nape of his neck, Reiner reflects on how close he had come with death, acknowledging that if he had taken even a little longer to move his brain functions to the rest of his body, he would have been killed instantly by Levi. Reiner then begins to wonder how the Corps had even thought to search inside of the Walls for him, coming to the assumption that it had been Armin's idea before discarding the subject entirely in order to focus on his mission. However, he is stopped in his tracks when he notices Erwin standing next to him atop the Wall, watching him calmly. Though surprised, Reiner elects to ignore him and instead focus on the killing the horses. He is stopped in his tracks once again, however, when Eren transforms behind him.

Watching from atop the Wall, Reiner is alarmed to see Eren's Titan form watching him from the ground. Reiner tries to deduce why Eren would reveal himself to his would-be abductors, but is surprised when, instead of attacking, Eren begins to flee. Reiner realizes that Eren intends to escape the battle by scaling the Walls in Titan form, and begins to panic as he imagines what would happen if Eren, who was able to master the Hardening ability in two months, were to escape and master the Coordinate. However, Reiner realizes something that puzzles him: it would make much more sense for Eren to scale the walls with his 3D Maneuver Gear before changing into his Titan form, rather than changing forms in the middle of Shiganshina District and calling attention to himself. It is at this moment that Reiner realizes that Erwin is using Eren as bait to lure Reiner away from the Corps' horses. Reiner is both appalled and impressed with Erwin's strategy, but decides to pursue Eren.

As Reiner follows him, Eren remembers Armin informing Hange's squad of Erwin's plan. Hange agrees with the plan, hypothesizing that Reiner will attempt to capture Eren, as allowing Eren to escape would give Eren the opportunity to flank the Beast Titan, and defeat him with the help of Levi and his squad. Hange insists that even if the plan doesn't go exactly right, the sight of Eren fleeing will throw the enemy off to the point that they will break their siege. Eren agrees, testifying that Reiner will be smart enough to predict their plan and pursue him. Before they begin, Armin reminds the squad that Bertolt is still hiding somewhere, and that Eren should engage Reiner away from the Walls so as not to be ambushed like he was the last time he fought Reiner.

As Eren and Reiner meet in the center of Shiganshina, Eren recalls his previous fight with Reiner while in Titan form, sure that he will be able to beat Reiner in a one on one fight again. The two begin to fight, each deftly avoiding each other's blows until Eren finally lands one mighty punch to Reiner's face, which smashes through his armor. As Reiner topples to the ground, Eren mentally notes that their battle ground is the town where he once lived, and that he will take it back by killing every single Titan.

As Eren and Reiner fight, Mikasa, Armin, and the rest of their squad approach, carrying with them new weapons attached to their Three Dimensional Maneuver Gear.

Trivia

 * Armored Titan climbing down Wall Maria.png is a big error in the proportions of the Armored Titan´s and Wall Maria's heights. The Armored Titan is 15 meters tall, while Wall Maria is 50 meters; that means the Wall is 3⅓ times taller; however, it is depicted as being much larger, at least 8 times taller than the Armored Titan as seen at the bottom right panel of page 30 (see the picture at the right), what would give a height of around 120 meters. Though Isayama usually draws Titans and buildings with errors in the proportions, in this case the error seems to have an influence in the plot, as the Armored Titan spends much of the chapter climbing the Wall despite getting up great speed before jumping.