Arknights takes place in a place not too different from ours-- major nations in our world have parallels in Arknights. Victoria, for instance, is a victorian-era UK. Columbia is US during the 1900s. However, there are a few major differences between our world and Arknights. First off, there are no regular humans. Everyone is a type of kemonomimi or furry.
Second off, there is a unique mineral, called Originium, that has a massive amount of uses owing to the fact that it has a high energy yield. Everything that would work on electricity or use an engine instead uses originium. However, it is quite volatile and and causes a disease called Oripathy. Oripathy is not only fatal, but those who die in the latter stages explode into a mist of originium. This has led to discrimination of those infected with it.
Third, there are a higher amount of natural disasters which are referred to as catastrophes. They leave behind large sources of originium. In order to avoid catastrophes, cities are built on large, mobile platforms. They are referred to as Nomadic Cities.
Lastly, the lack of gunpowder has made most people stick with swords, bows, and crossbows. Although, explosives aren't too hard for normal people to use. There is also Originium Arts, a type of magic. Originium is used in wands to boost the power of arts, as otherwise a person's arts would be considerably weaker. Guns are trickier and only the angel people of Laterno have a natural ability in using them. Bullets are etched with small originium circuits and require a precise amount of focus.
Speculated Arknights Timeline (Not Mine)
THIS IS A SPECULATED TIMELINE.
Thanks to 邪恶天才 on bilibili for a lot of the sources, and thanks to the many pals on the Arknights Discord #ak-lore channel for corrections.
This timeline assumes the HoSF date of 1097 as the current date.
These dates are approximate as wars and such could last many years.
1077: Ursus-Lungmen conflict (Main 5-11, Wei mentions a conflict 20 years ago).
1090: Siracusa incident (Code of Brawl CB-7, Capone mentions their leader being assassinated which led them to come to Lungmen).
1093: Kazdel civil war (Anonymous Ones’ War, Scout mentions 3 years ago Rhodes/Doctor joined in the civil war).
1093: possible date of Doctor’s disappearance (Anonymous Ones’ War, Scout says people hope to have the Doctor back, because they have lost so much).
1096: Grani and the Knight’s Treasure event (Grani has 2 years of combat experience before joining Rhodes).
1096, before December 23rd: prior to Doc’s rescue mission (Blaze’s lines in Main 6-2, when Ace was still alive).
1096 December 23rd: possible date of Reunion’s attack on Chernobog (Tutorial introduction mentions December 23rd, which is also Amiya’s birthday).
The following assumes 1096 December 23rd as the date of the Chernobog invasion.
1096 December 27th: Doc’s trip to Lungmen (TR-11 mentions 4 days after Chernobog mission, and Closure asking if they’re going to Lungmen in OI).
1096-1097 Spring: Events of Separated Hearts (Main 2-6, Misha says she’s been in Lungmen for a week, and it is likely she was in Chernobog before).
1096-1097 Spring: After Misha’s death, Rhodes Island docks near Lungmen.
1097 Spring: Lungmen invasion, speculated to happen shortly after RI’s docking.
1097 Summer: Heart of Surging Flames event (Makes sense since Blaze was injured at the end of Chapter 6, and by HoSF she is still recovering).
No specific dates given after Chapter 3.
Code of Brawl: happened after the Lungmen invasion since they mention visiting the grave of Ch’en’s informant. CoB should also occur during Fall from the Halloween reference.
Ancient Forge: sometime before AK equivalent of Chinese New Year. Nian’s talk with Closure at the end of AF reveals that Alty’s visit to Kal’tsit at the end of HoSF was before AF. Since CNY happens in January, AF must’ve happened in 1098.
Thanks to 邪恶天才 on bilibili for a lot of the sources, and thanks to the many pals on the Arknights Discord #ak-lore channel for corrections.
This timeline assumes the HoSF date of 1097 as the current date.
These dates are approximate as wars and such could last many years.
1077: Ursus-Lungmen conflict (Main 5-11, Wei mentions a conflict 20 years ago).
1090: Siracusa incident (Code of Brawl CB-7, Capone mentions their leader being assassinated which led them to come to Lungmen).
1093: Kazdel civil war (Anonymous Ones’ War, Scout mentions 3 years ago Rhodes/Doctor joined in the civil war).
1093: possible date of Doctor’s disappearance (Anonymous Ones’ War, Scout says people hope to have the Doctor back, because they have lost so much).
1096: Grani and the Knight’s Treasure event (Grani has 2 years of combat experience before joining Rhodes).
1096, before December 23rd: prior to Doc’s rescue mission (Blaze’s lines in Main 6-2, when Ace was still alive).
1096 December 23rd: possible date of Reunion’s attack on Chernobog (Tutorial introduction mentions December 23rd, which is also Amiya’s birthday).
The following assumes 1096 December 23rd as the date of the Chernobog invasion.
1096 December 27th: Doc’s trip to Lungmen (TR-11 mentions 4 days after Chernobog mission, and Closure asking if they’re going to Lungmen in OI).
1096-1097 Spring: Events of Separated Hearts (Main 2-6, Misha says she’s been in Lungmen for a week, and it is likely she was in Chernobog before).
1096-1097 Spring: After Misha’s death, Rhodes Island docks near Lungmen.
1097 Spring: Lungmen invasion, speculated to happen shortly after RI’s docking.
1097 Summer: Heart of Surging Flames event (Makes sense since Blaze was injured at the end of Chapter 6, and by HoSF she is still recovering).
No specific dates given after Chapter 3.
Code of Brawl: happened after the Lungmen invasion since they mention visiting the grave of Ch’en’s informant. CoB should also occur during Fall from the Halloween reference.
Ancient Forge: sometime before AK equivalent of Chinese New Year. Nian’s talk with Closure at the end of AF reveals that Alty’s visit to Kal’tsit at the end of HoSF was before AF. Since CNY happens in January, AF must’ve happened in 1098.
Anima has enough flexibility and animu in it to accurately represent Arknights. Although flying around with ki isn't exactly canon in any instances.
I borrowed a few explanations from https://mrfz.fandom.com/wiki/Arknights_Wiki since I felt like they explained it best and probably know things better than me.