Attack on the Sorcerer Kingdom's Transport was an attack orchestrated by the Re-Estize Kingdom's New Faction on a merchant carriage from the Sorcerer Kingdom, in hopes of eliminating their competition. However, it instead became the spark that would lead to war between the two nations.
Meanwhile, The Sorcerer Kingdom had already begun plotting to conquer the Kingdom; a plan Sorcerer King Ainz codenamed "Candy & Whip." It involved manipulating a noble into revolting against the Kingdom, which would give the Sorcerer Kingdom a casus belli to invade. Before this though, they would earn the citizens' trust to make them more accepting of their "intervention."
While on a diplomatic visit to the Kingdom, Prime Minister Albedo met a low-ranking noble named Philip, who she saw would make a perfect pawn. To prop him up, she had Eight Fingers gather upstart nobles to form a New Faction, with him as the leader. She also had the criminal organization export massive amounts of food from the Kingdom to further dwindle supplies. Not long after, the Sorcerer Kingdom began importing their own product.
Contrary to Albedo's plans, however, the influx of food interfered with Philip's plans to inflate his prices, causing him to turn on his benefactors. Together with fellow New Faction members Wayne and Igor, he plotted to rob the carriages transporting the food and sell the contents as their own. While two initially did not want to participate, foreseeing the consequences, they calculated that the Sorcerer Kingdom should only have the manpower to annex regions close to the border in case of a war of retribution, far away from their domains.
In preparation for the attack, Philip drafted 50 peasants of his domain while Wayne and Igor both drafted 75. Philip and his men would attack first, while Wayne and Igor's forces stayed back. Unbeknownst to Philip, this was so the two could minimize their losses.
The "attack" was over before it even began, as the merchants and mercenaries transporting the carriages felt no loyalty to the Sorcerer Kingdom. Thus, upon seeing Philip and his force, they immediately gave into his demand to stop and hand over the transport.
Wayne and Igor soon arrived at the scene and expressed shock at how easy it went. As agreed, Philip would take 80% of the caravans' contents while Wayne and Igor each got 10%. However, Wayne and Igor wanted nothing to do with an incident that could spark a war and offered to have Philp have all the spoils, though he insisted they have their share.
Due to all passengers being Eight Fingers members, the Sorcerer Kingdom quickly learned of the attack. Albedo blamed the organization for losing control of Philip and brought his overseer, Hilma Cygnaeus, in for questioning before Sorcerer King Ainz Ooal Gown himself. However, he ultimately led her and the organization off once it became clear they had no involvement in the attack.
Albedo and Demiurge believed that the attack was part of a larger plot. However, when Ainz brought up the notion that Philip simply hadn't thought the consequences through, the Floor Guardians immediately sided with their master's "deduction." Regardless, the Sorcerer Kingdom now had a casus belli to invade the Kingdom and send them a declaration of war.
After receiving the declaration of war, the Re-Estize Kingdom's leadership gathered for an emergency meeting. However, they believed Philip was brainwashed by the Sorcerer Kingdom. Thus, rather then punish him, he was placed under protection. The only one who believed Philip should still be trialed was Second Prince Zanac, in hopes of appeasing the Sorcerer Kingdom. However, this idea was shot down by King Ramposa III.
Still, given the difference in military strength, the Kingdom's leadership knew they had to sue for peace. The meeting was interrupted, however, by news that Albedo would be visiting the Royal Capital. Taking advantage of this, during the royalty's audience with her, King Ramposa III offered his own life to the Sorcerer Kingdom to defuse tensions. Unfortunately, Albedo declared that the Sorcerer Kingdom would not settle for vassalization or peace offerings and that they would invade in one month.
Thus, with no other options, the Kingdom began preparing for war. However, unbeknownst to the leadership, the one month preparation time the Sorcerer Kingdom had given was an elaborate ruse. In reality, while the Kingdom prepared, the Sorcerer Kingdom had already begun their invasion in secret.