Attack on the Sorcerer Kingdom's Transport

Attack on the Sorcerer Kingdom's Transport was an attack orchestrated by the Re-Estize Kingdom's New Faction on carriages transporting humanitarian aid from the Sorcerer Kingdom to the Roble Holy Kingdom. It would end up being the spark that led to war between the two nations.

Operation Carrot & Stick
Following the Massacre at Katze Plains, the Royal Army had been devastated. Thus, the Re-Estize Kingdom had no choice but to avoid any sort of conflict while they recovered their strength.

Meanwhile, The Sorcerer Kingdom had already begun plotting to conquer the Kingdom; a plan Sorcerer King Ainz codenamed "Operation Carrot & Stick." It involved creating an artificial famine that would cause the nation's citizens to revolt and manipulating a noble into organizing said revolt, which the Sorcerer Kingdom would use as 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 deemed to be 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 organization steal massive amounts of food from the Kingdom while the Sorcerer Kingdom began exporting its own, much cheaper goods. This way, the Kingdom soon became reliant on the Sorcerer Kingdom for its food supply. All that was left now was to wait for the Kingdom's own supply to run out, at which point the Sorcerer Kingdom would raise prices to the point of unaffordability, resulting in famine.

Planning the Attack
Contrary to Albedo's plans, however, the influx of food interfered with Philip's scheme to inflate his prices. As a result, he immediately turned on his benefactors upon learning from fellow New Faction members Wayne and Igor that they were the source of his plight. Working together with them, he hatched a plot plotted to rob the carriages transporting the food and sell the contents as their own, believing that he would be viewed as a "Hero" for stepping up against the Sorcerer Kingdom and further boosting his sales.

Unbeknownst to Philip, however, he was being manipulated by the two. Seeing the Kingdom's current reliance on the Sorcerer Kingdom, Wayne and Igor hoped that this attack would discourage the latter from continuing to trade with them. Philip was to be their scapegoat who would bear all the consequences of the attack. Even if there were a war of retribution, they had calculated that the Sorcerer Kingdom should only have the manpower to annex border regions, far away from their domains.

In preparation for the attack, Philip drafted 50 peasants of his domain while Wayne and Igor both drafted 75. The plan was to use a "crane wing formation": Philip and his men would attack the carriages from the front and slowly retreat, allowing Wayne and Igor to flank the enemy from the sides. Unbeknownst to Philip, this was also so the two could minimize their losses and potentially turn on him in case the attack failed.

Incident
The "battle" was over before it even began, as the leader of the Eight Fingers members transporting the carriages, Christopher Olson, believed this to be yet another act of infighting between the organization's divisions; thus, not wanting to risk his and his subordinates' lives over something so seemingly trifling, he gave into Philip's demand to hand over the transport and fled the scene with his men.

Aftermath
Once Philip had secured the transport after its guards had fled the scene, Wayne and Igor arrived and expressed shock at how easy it went. As agreed, Philip would take 80% of the spoils while Wayne and Igor each got 10%. However, the two wanted nothing to do with an incident that could spark a war and offered to have Philp have all of it, though the latter insisted they have their share.

Investigation
Due to all passengers surviving and 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 himself. However, the monarch ultimately led her and the organization off once it became clear that they were not involved in this.

Albedo and Demiurge believed the attack to be part of a larger plot. However, when Ainz brought up the possibility that Philip simply had not thought the consequences through, the Floor Guardians immediately sided with their master's "deduction", which ironically ended up being spot on.

Regardless, Philip's actions showed him to be an unreliable pawn; thus, the Guardians decided to scrap "Operation Carrot & Stick". However, believing this to be a waste, Ainz questioned his subordinates whether something could still be salvaged. This offhanded remark causes the Guardians to come to a delusional conclusion: the attack was actually all part of their master's plan and the true aim of "Operation Carrot & Stick" was to destroy the Kingdom to threaten other nations not to antagonize them. The Sorcerer Kingdom thus declared war on the Kingdom, using the attack as a casus belli.

Resulting War
After receiving the declaration of war, the Kingdom's leadership gathered for an emergency meeting. Given the difference in military strength, they had to sue for peace. Thus, when Albedo visited the Royal Capital, King Ramposa III offered up his own life to defuse tensions. Unfortunately, Albedo declared that they would not settle for vassalization or peace offerings and that they would invade in one month. In reality, though, this was an elaborate ruse and the Sorcerer Kingdom began their invasion immediately.

Despite causing an incident that sparked a war, rather than facing punishment, the New Faction was placed under protection, as it was believed they were [Charmed]. However, they soon experienced their own kind of punishment: as the war with the Sorcerer Kingdom got worse and worse, they found themselves wrought by guilt for causing such a disaster and they finally paid retribution when their former benefactors silenced them to erase evidence of "Operation Candy & Whip."

In the end, Wayne and Igor's calculation ironically ended up being correct in a way: the Sorcerer Kingdom lacked the manpower to conquer the Kingdom, so they destroyed the nation instead.

Trivia

 * The anime only features Philip, Igor, and Wayne planning the attack and its aftermath, skipping over the incident itself.