1. This is a 3 year time-skip after the Survey Corps visit the ocean. 4 years after the Battle of Shiganshina.
2. Marley is in war with the Middle-Eastern Union, which was triggered 4 years ago, after they lost the Colossal and the Female Titan.
3. The Marley is looking for successors for the powers of the Armored Titan and Beast Titan. So this chapter describes 4/5 such Warrior candidates being sent to the front-lines of the war as a final test.
to be more precise:
In Marley's operation to take the Founding Titan from the royal family of Paradis, their mission was met with failure. Not only were the warriors unsuccessful in taking the Founding Titan, but the Female Titan and the Colossus Titan were lost during the Stohess District raid and the battle of Shiganshina District, respectively. With the loss of two Titans, Marley's military capabilities were greatly reduced. This loss of power was noticed by the Mid-East Allied Forces, a coalition of territories against the nation of Marley, and thus war was declared in the year 850 which is now known as the Marley Mid-East War.
The Marley Mid-East War is an ongoing conflict between the nations of Marley and the Mid-East Allied Forces on the continental mainland.
While the specific events of the war between Marley and the Allies are unknown, Marley successfully gained the upper hand over the Allies over the course of four years. A significant portion of the combat took place on the sea, where Marley slowly pushed back the Allies' fleet and gained control of the waters. However, the naval battles were evidently poorly fought, as Marley had lost over half of its navy during these four years.
Anyways, great chapter...... now we know the other side of the ocean's story and what Reiner and Zeke been going through.
