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According to Marley history textbooks, Marley was a powerful nation in ancient times. However, over 1,800 years ago, the dominion of Marley was threatened when Ymir Fritz, a queen of the Fritz family who ruled the "Subjects of Ymir", came in contact with the "source of all organic material" and gained the power of the Titans. After Ymir's time, her "soul" was split into nine Titans who inherited her power and formed the Eldian Empire. With the power of the Titans, the Eldians waged war against the Marleyans, utterly destroying their nation and obtaining complete rule over the continental mainland. Over the course of 1,700 years, the Eldians would designate all other races of the world as inferior and resort to genocide and rape in order to cleanse the world of other peoples.
Many centuries after Eldia's ascension to power, the 145th King of the Fritz family inherited the power of the Founding Titan, the greatest of all Titans. Rather than maintaining order in Eldia as his forebears had done, the King chose instead to relocate the capital of Eldia to the remote island of Paradis. In the King's absence, the surviving peoples of Marley rose up against their oppressors, starting the Great Titan War. At this time, Marley succeeded in obtaining seven of the nine Titans in Eldia's possession, drastically turning the tide of the war. Over an unspecified amount of time, Marley gradually gained control of the continental mainland that once was ruled by Eldia until only Paradis remained as King Fritz's undisputed territory. At this time, in the year 743, King Fritz used the Progenitor Titan to guide countless Colossus Titans in the raising of three concentric Walls, Maria, Rose, and Sheena, around Eldia's remaining territory. In order to force peace between Eldia and Marley, King Fritz gave the ultimatum that any further act of war against Eldia would be met with the releasing of the countless Titans within the Walls. With this, the Great Titan War ended.
The Marleyan society is technologically more developed comparing to the Eldian society within the Walls. Modern marvels such as photography are commonplace to the general population. There are also civil transports powered by battery and fossil-fuels, such as automobiles and blimps, although the latter seem to be available only to the wealthy, non-Eldian population. Electricity seems to be in use, as there are loudspeakers mounted on the Walls surrounding the Liberio Internment Zone. Marley seems to be an industrialized nation, as there are factories in the proximity of the Zone.
Moreover, Marley has developed in recent years, inventing steam-powered warships, triplanes, possible rail-based transports, as well as some sort of transport aircraft used to parachute soldiers into the battlefield.
Titan Chemistry Research Society
The Marley government has vast knowledge of the Titans to the extent that they are able to make use of Titan-related technology and possess insight as to the origin of the Titans. For example, the Marley government are known to create Titan serums for use in creating the warriors and as a tool to transform Eldian criminals into Titans on Paradis.
An academic discipline known as "Titan chemistry", headed by Marley's Titan Chemistry Research Society, was founded in dedication to the research of Titan. It is the Society that put forth the theory that all Eldians are connected by unseen "paths" from which the flesh and bones of Titan are sent to them, and that all the paths "coordinate" at the Founding Titan.
Eldian minority in Marley
After the Great Titan War, the Eldians who remained on the continental mainland were designated as low-class citizens. Rather than resorting to genocide, the Marleyans were aware of the military potential of the Eldian's genetic trait, and chose instead to segregate the Eldians from the rest of the population into the Liberio Internment Zone under the watch of the Public Security Authorities, so that they may be converted into pure Titans for use as a reserve force in war. 
In later years, however, the use of mindless Titan became controversial within Marleyan military circle, as it is inherently uncontrollable and poses as much a risk to the enemy as to itself, leading to opinions for the extermination of all Eldian. Kruger noted that once Marley secures the Founding Titan, the debate would end in favor of those opinions and seal the doom of all Eldian.
To justify its exploitation of Eldian, the Marleyan government indoctrinated its citizens with revised history which blamed Eldian for supposed past acts of genocide against them. As a result, the Marleyan populace saw the Eldians as inferior by blood due to their ancestor Ymir Fritz's deal with the "Devil of All Earth". On the other hand, average continental Eldians, such as Mr. Yeager and Gabi, became convinced that they were genuinely indebted to their "merciful" Marleyan overlord. In the latter case, Gabi even went so far as to believe that the only way to redeem her people on the continent is through the extermination of "bad" Eldian on Paradis.
The Marleyan government determines the ethnicity of its citizens with blood test, and the result of which affects their eligibility to get into privileged professions. To join the Public Security Authorities, for example, one has to prove that they are not of Eldian ancestry by passing the test. Despite that, agents of the Eldia Restorationists were able to get around it by using falsified medical records and having their tests done by doctors sympathetic to their cause.
Marley maintains its military dominance in the world stage by the use of Titans and a technologically advanced military force which is comparable to a real life WW1-era military.
In the year 854, the Marleyan Army saw major action during the four years long war against the Mid-East Allied Forces.
Having made incredible advancements in military technology in the years following the Great Titan War, the Marleyan Army possesses a powerful armament of semi-modern weapons. In term of small-arms weaponry, bolt action rifles and stick grenades are the standard-issued weapons of Marleyan infantrymen. Zeke also carries a sub-machine gun into battle, suggesting that automatic small-arms were used at least by Marley's elite airborne unit. Heavier weapons such as Maxim-style machine guns were employed as the primary armament of certain Titans, turning them into mobile weapon platforms. 
The use of Titan is central to the Army's doctrine. Beside having the seven Titans as strategical deterrents, Marley also has a long-standing strategy of converting its Eldian population into pure Titans to bolster its military strength. In ancient time, pure Titans were simply set loose before friendly line toward an enemy force en masse, as they are unable to follow complex commands except from the Founding Titan. The tactic remains unchanged in the modern era, except that the Titans are now airdropped by zeppelins.
Other than strategic value, Titan shifters also fulfill the tactical role of real-life tanks on the field. For example, Galliard was tasked to destroy a machine gun nest which was otherwise untouchable by infantry in the battle against Fort Slava; A more literal example is Pieck, who had four machine gun turrets strapped on his back, a configuration that proved highly effective in clearing the Allies' trench system. Otherwise, Marleyan infantry practices conventional tactics such as trench warfare, frontal human wave assault, and rudimentary anti-armor technique such as the use of bundle stick grenades.
While its organisation remains unclear, it is known that candidates of the warrior program are embedded into the Army as cadets, and front-line service was part of their selection process. 
Ethnic segregation probably exists in the army as it does in the civilian society, and is reflected in the servicemen's equipment. Like in civilian life, Eldian soldiers are required to wear the armband signifying their ethnicity. They are also issued with Pith helmet-like headgears which have their ethnic symbol pinned on it, while Marleyan soldiers wear Stahlhelm-like helmets. Nevertheless, the difference in gears may have the purpose of denoting ranks and have nothing to do with segregation. Even though they have shared experience on the battlefield, Marleyan servicemen still hold grugde against their Eldian "comrades".
The Army seems to have little regards for proper conducts of war. For example, Army Commander Magath intentionally allowed Gabi to attack an enemy bunker in civilian guise, even though he was aware of that it violates international laws.
The Marleyan Navy is the sea-faring branch of the nation's military force.
During the Marley Mid-East War, It only managed to control the sea at the cost of half of its fleet after four years of fighting. Relations between the Army and the Navy are poor, with warrior cadet Udo scolding it for being a "cesspool of incompetence".
In the year 830, the Navy was mentioned to possess steam-powered ironclads. By the year 854, Udo mentioned that "battleships" were deployed in the naval war against the Allies. Given that the Allied possesses dreadnought-style warships, it was possible that the Marleyan naval technology has also progressed by that point.
Before the year 830, Marley possessed seven Titans which assured its position as a world power. This power was eclipsing, however, as advancement in technology are beginning to undermine the military importance of Titans. The Marleyan government is aware of it, therefore it planned to conquer Eldia in order to take over the immense fossil resource laying beneath the island, continuing its military supremacy in the new era. The plan was hindered by King Fritz's threat of unleashing the Wall Titans upon the world in case of a Marleyan invasion.
In order to counter King Fritz's ultimatum, the Marleyan government decided to grant the power of the seven Titans in their nations possession to a selection of Eldian children. The families of those chosen children were promised to be made into honorary Marleyans with all freedoms that come with the distinction. These children were trained into expandable soldiers in warfare while also serving as candidates to inherit the powers of the Titans.
Over a dozen years later, in the year 845, Marley sent out four of their warriors, Bertolt Hoover, Reiner Braun, Annie Leonhart, and Marcel, from their settlement known as the "Hometown". These warriors were given the task of breaching the gates of the Walls in order to wipe out the Eldian race and take the Coordinate, or Founding Titan, from the royal family. They succeeded in breaching Wall Maria, though their efforts in breaching Wall Rose were halted upon learning that Eren Yeager possessed the power of the Titans, leading them to suspect that he held the Coordinate they sought. Since that revelation, the goal of the surviving warriors has been to capture Eren Yeager in order to obtain the Coordinate. However, after their failure at the battle of Shiganshina District, the plan to regain the Founder has since been postponed due to the loss of the Colossus and Female Titans.
In the year 854, a warrior cadet unit consisting of Gabi, Falco, Colt, and some 800 other cadets was sent to capture Fort Slava under the command of Commander Magath during the Marley Mid-East War. The same battle also saw Reiner and Zeke being deployed on the field alongside a barrage of mindless Titan. Reiner was severely damaged when he shielded Zeke from a direct hit of a naval artillery shell.
The Public Security Authorities is a Marleyan internal military force. Its primary purpose is to control Eldian minority within the Marleyan mainland. The PSA repression against Eldian drove Grisha Yeager into becoming an Eldian Restorationist and directly led to the creation of several named Titans which ravaged the Walled society in Paradis, setting in motion the manga's story.
Politics and Diplomacy
Marley has historically had a poor relationship with the Mid-East Allied Forces. By the year 850, after it had become known that Marley lost two Titans in its operation against Paradis, the Allies finally declared war against Marley. Over twenty years ago, the Eldia Restorationists had considered using the Founding Titan to gain support and defection from this enemy nation, though their efforts failed.
- Marley resembles Nazi Germany in both its general aesthetics and politics but its technological development is slightly less advanced, being at around early 20th century level.
- Marley's policy of segregating Eldian into ghetto parallels Nazi anti-Jewish policy. Coincidentally, some named Marleyans and Eldians have German-sounding names.
- The history of Marleyans and Eldians is also comparable with that of the Rwandan populations of Hutu and Tutsi. By 1700, the Rwandan populace coalesced into around eight kingdoms, of which the Tutsi Kingdom of Rwanda became dominant and oppressed the Hutu, fueling a hard relationship between the two races that lasted for centuries. In 1994, during the Rwandan Civil War, the then Hutu majority government perpetrated a genocide against the Tutsi which resulted in the extermination of around 70% of the Tutsi population.
- Rwanda was also a German territory from 1884 until World War I.
- Since Isayama is Japanese, the Marleyan government's exploitation of ancient grudges for expansionist purposes might have been inspired by the anti-Japanese sentiment in China, where the memory of the Second Sino-Japanese War is kept alive by the government for nationalistic purposes. The landmass size difference between Marley and Paradis also reminds one of China and Japan.
- The memory alterations to people on Paradis to make them forget the past might have been inspired by the Japanese government's own attempts to downplay and deny Imperial Japan's war crimes.
- If turned upside-down and mirrored, the territories of Marley and Paradis are very similar to the real life continental territory of Africa and the island of Madagascar, respectively.
- This also coincides with the Rwanda parallelism, as Rwanda is a country within the mainland of Africa some distance northwest of Madagascar. When turned upside-down and mirrored, Rwanda is at the southwest, and it is said that Titans primarily target the southern regions of the Walls (although the exact location of Marley within the continent is still unknown).