Anti-Sorcerer Kingdom Alliance

Anti-Sorcerer Kingdom Alliance is a hypothetical coalition of multiple nations against the Sorcerer Kingdom. The Baharuth Empire attempted to form it with the Slane Theocracy and the Re-Estize Kingdom with the Argland Council State, but both nations ended up being annexed before talks could be finalized.

Background
It is an alliance that is comprised of different nations in the New World continent that act collectively as an opposition to the Sorcerer Kingdom. In this alliance, countries are looking to combine their forces together collaboratively and militarily against a very powerful enemy who is stronger than them. As an alliance, they are focused on working to stop the Sorcerer Kingdom and whatever nefarious plans it is secretly plotting such as its world domination agenda that remains undisclosed to the New World but Nazarick. They commonly viewed the Sorcerer Kingdom as the biggest threat that endangers the lives of surrounding countries.

However, due to the immense intelligence and foresight of Nazarick's Demiurge and Albedo, and various other coincidental events and the immense power of the Sorcerer King, any attempts to actually form the alliance has been completely stopped before they could ever seriously form by any of the major human/demi-human nations. Making the chances of an alliance that might even genuinely possess a threat to the Sorcerer Kingdom unlikely.

The Magic Caster of Destroy Arc
After the Baharuth Empire propose a false alliance with Nazarick, they under Bloody Emperor Jircniv's rule silently seeks to form a grand coalition with other countries, aimed at defeating Ainz Ooal Gown and the Sorcerer Kingdom it plans to make. Particularly, Jircniv wants the Baharuth Empire, the Re-Estize Kingdom, the Slane Theocracy, the Argland Council State, the Roble Holy Kingdom and other countries so forth to come together in an alliance, where they can defeat their common enemy. Jircniv orders his imperial servants to secretly prepare for the survival of humanity and the world.

The Ruler of Conspiracy Arc
On one such secret exchange, he learns that the High Priests and representatives from the Slane Theocracy have agreed to meet with him secretly at the Grand Arena. During this secret meeting with the emissaries of the Theocracy and the high priests from the temples, Jircniv is planning to establish talks about having the Empire side with the Theocracy. However, before he could conduct talks, Jircniv is left utterly shocked by discovering the presence of Ainz Ooal Gown in the Empire and him being the Martial Lord's challenger in the Grand Arena, where his meeting was supposed to successfully takeoff. With the Sorcerer King in close vicinity of their back-door meeting, the Slane Theocracy opts to abandon it. The High Priests nearly follow suit but are prevented by Jircniv who pleads them to wait and watch the fight between the Go-Gin and Ainz happen, hoping to see the undead lose while finding its weaknesses. Sadly, not everything went according to his plans or expectations as it was the Martial Lord who ended up losing in the end. When Ainz finally went to confront the emperor directly, Jircniv realizes that it is no longer possible for the Empire to establish an alliance with the Theocracy, seeing that all his possible allies vanish before him.

The Witch of the Falling Kingdom Arc
Prince Zanac and Princess Renner hold a discussion on whether to abandon the plans on forming an alliance with the Argland Council State. According to them, while the creation of an alliance is currently in progress, they felt the situation isn't looking great for the Re-Estize Kingdom. Though a Dragon Lord from the Argland Council State has agreed to it, the two are still in need of more time to convince the representatives of the other races. Even if this falls through, they believed that the prospect of an alliance would not be completely ruled out, that much was said. They described that the Anti-Sorcerer Kingdom Alliance was forming at a snail’s pace, but progress was going smoothly nonetheless. The Re-Estize Kingdom was at the stage of relying on the generosity and solidarity of other countries to hopefully get them to sign the mutual reinforcement pact at all costs, in other words, it was an unreliable relationship without written agreements. Something like that could not be publicly announced as a military alliance. There were simply so many things to do and prepare for in order to form a tight alliance against the Sorcerer Kingdom, they would need at least a few months to have it sorted out.

However, anticipating the potential alliance between the Argland Council State and the Re-Estize Kingdom, the Sorcerer King and his subjects secretly invaded the northern half of the Re-Estize Kingdom. Thus cutting off the council due to the north containing their border with the Kingdom, simultaneously preventing the Council State from assisting and sending reinforcements to the Kingdom and successfully isolating the Royal Capital. It also placed pressure on the Council State by implying that the Sorcerer Kingdom knows full well of their secret talks of an alliance against them and subtly warning the Argland Council to stay clear of their war with the Re-Estize Kingdom. Once again successfully foiling the formation of a combined coalition army against the inhuman nation.

Strength
So far, no information was ever revealed about who or what nation is going to be and will end up joining the Anti-Sorcerer Kingdom Alliance. At the same time, whether such alliance currently exists remains unknown as none right now appear to have been successfully created. For instance, the alliance Jircniv proposed was the first of its kind known to have ended in total failure.

Trivia

 * Bloody Emperor Jircniv was unsuccessful on creating an Anti-Sorcerer Kingdom Alliance with the Slane Theocracy due to the interference from the Sorcerer Kingdom, particularly the Sorcerer King Ainz Ooal Gown.
 * Before the Baharuth Empire became a vassal state to the Sorcerer Kingdom, the fact that Jircniv suggests having a non-human nation like the Argland Council State into the alliance composing of namely human countries mentioned by him presumes he was likely also trying to get more non-human countries to join as well.
 * According to Maruyama's conversation with the interviewer, there are multiple countries in the middle of the continent and that they will eventually make an alliance. He said they will work together to fight against the Floor Guardians in a huge war.
 * Maruyama noted that if he ever expands the Overlord Light Novel to 30 volumes, it would get into the war with the alliance of countries in the center of the continent. Maruyama stated that he doesn't want to push for more volumes because then he'll end up having to write about the war with the alliance of central countries.
 * The Re-Estize Kingdom and the Argland Council State have initiated talks in order to join forces to combat the growing threat of the Sorcerer Kingdom during the events of Volume 14, but the talks themselves are slow due to the Council's hesitance to team up with the failing/corrupt state.
 * Eventually the chances of an actual alliance forming between the two nations became even more unlikely due to the incident that triggered the war between the Sorcerer Kingdom where a single Foolish Nobleman had stolen a grain transport meant for humanitarian aid for the war ravaged Roble Holy Kingdom, making the Argland Council even more hesitant to become allies with the Kingdom due to them being technically the ones to start the war and the sheer stupidity of the Nobleman in question only cemented their belief in the sheer incompetence of the Kingdom's leadership and showing that the failing state's failure can not give them any genuine benefits or merit in teaming up together.
 * Eventually the chances of the Argland Council forming an alliance with the Kingdom is completely squandered due to the fact that the Sorcerer Kingdom successfully conquered the Northern part of the Kingdom that contained the Kingdom's border with the Argland Council State and successfully cutting off their contact with council as well as subtly pressuring and threatening the Council from interfering with their war.
 * The Roble Holy Kingdom, hearing about the Sorcerer Kingdom and the Undead/Demi- Human/Heteromorph inhabitants and its powerful undead ruler, began making plans to team up and ally with the Slane Theocracy to combat and defeat the Sorcerer Kingdom due to their prejudice of the non-human Nation and biased fear of the undead.
 * However due to the invasion caused by Jaldaboth and slaughter of a majority of its Northern territory and the apparent selfless rescue done by the Sorcerer King to save them and the formation of the Cult-like following made by Neia Baraja that idolize the Sorcerer King; its now highly unlikely that an actual alliance will ever form between the Slane Theocracy and the Holy Kingdom. Especially since unknown to the populace; the Sorcerer Kingdom have already placed a hidden puppet ruler on the Holy Kingdom Throne.
 * Eventually Neia's cult continued to grow in size and influence due to the sheer popularity of it in the Northern Half of the Holy Kingdom that by the time of Volume 14, Neia had already implied to have successfully usurped the authority of the Holy Kingdom's religious institution or has now obtained authority and power far surpassing the religious system. As seen where Neia's personal seal was stamped right next to the Holy Kingdom's symbol declaring of their approval of the Sorcerer Kingdom's war against the Re-Estize Kingdom.
 * This in turn makes it even more unlikely for the Roble Holy Kingdom to unite with the Theocracy against the Sorcerer Kingdom due to their now completely opposing religions.