Given the difference in military might and unlikelihood of receiving foreign aid, since their nation technically instigated the war, the Kingdom's desperately tried to sue for peace. However, despite King Ramposa III going as far as to attempt to offer up his own life to try to appease Sorcerer King Ainz Ooal Gown, the Sorcerer Kingdom's prime minister, Albedo, merely stated that the war would proceed in one month.
Thus, despite knowing they did not stand a chance, the Kingdom began preparing for war. However, this only applied for territories who were likely to be within the armies' path. On the other hand, regions that would likely only be effected by the time the Royal Capital had already fallen did not even bother to evacuate the civilians or build fortifications.
Unfortunately for the Kingdom, the date the Sorcerer Kingdom had given for the start of their invasion was all an elaborate ruse. In reality, while the Kingdom prepared, the Sorcerer Kingdom secretly marched their armies over the border and began invading those territories that thought themselves to be outside the line of fire. Like this, the Sorcerer Kingdom easily conquered the Kingdom's western and northern regions, cutting the nation off from it's last remaining ally, the Argland Council State, and isolating the Royal Capital. Then, they massacred all the inhabitants and halted the flow of information out of these regions, causing the Kingdom's leadership to have no idea that the Sorcerer Kingdom had already begun their invasion.
To complete their encirclement, the Sorcerer Kingdom targeted the port city of E-Naüru. Before this, however, news of the invasion had finally leaked out when a noble escaped his territory just before the Sorcerer Kingdom attacked and made it to the port. In response, messengers were send throughout the region and an evacuation order was given. A few days later, the Sorcerer Kingdom's armies arrived and the battle began.