Unification
By the winter of 1586, peace had returned to the empire of Japan, as all the lords of the Great Clans, the Uesugi, the Shimazu, the Mori, the Otomo and so many others fall under the banners of the Takeda Clan and the marching armies of Takeda Katsuyori.
But even as the daimyo of Kai returns to Kyoto in the spring of 1587 at the head of an ever victorious conquering army, a small quarter of the nation remains independent from the central government at the Imperial Capital: the North.
Beyond the western borders of the Takeda and Uesugi domains at Echigo and Kanto, beyond the control of the great lords of central and western Honshu, the local clans acted with great autonomy and in many times with indifference to events in the central provinces, even as Takeda Shingen and Katsuyori began their quest to bring the nation under one banner.
The destruction of the Hojo and the Uesugi, the return of the Uesugi to the Kanto, all served as signs to show them the shape of things to come. The northern provinces of Dewa and Mutsu were ruled by several warring clans including the Ashina, the Date, the Nambu, the Hatakeyama, the Mogani and several others.
Two reasons explain why Takeda Katsuyori didn’t bother to subdue the region and its daimyos, or even care about Dewa and Mutsu until the summer of 1588.
Firstly, the Takeda were always preoccupied with more immediate concerns and threats. Following the war against the Uesugi and the Hojo in the 1570s, the Takeda faced the new administrative and military challenges of controlling such a large domain, and then a war against the Mori and the Shimazu. And once this new menace was dealt with, Katsuyori was forced to spend considerable time in Kyoto dealing with the administration of a unified Japan.
Secondly, the region lacked any significant political or economic importance that could have warranted the attention of the Takeda Daimyo. It was the personal ambition of Katsuyori, the goal of having the entire nation under his control, what drove him to the northern confines of Honshu in 1588.
Now, as opposed to the bloody wars against the Oda, the Uesugi and the Mori, or the shorter military campaigns against the Shimazu and the Chosokabe, marching from Kyoto to Sendai was more of a political show of will than a military show of strength.
Having destroyed the greatest armies that the rivaling clans could yield on the field, there were no battles left to fight, no one to resist. By July of 1588, the hegemonic power in Mutsu was a Daimyo by the name of Date Masamune, a resourceful and intelligent tactician known as the “One-Eyed Dragon.”
In the years spent between 1573 and 1588, the fight for supremacy in northern Japan had devolved in a two-way war between the Date led by Masamune and whatever coalition was formed to stop him, generally led by the rival Ashina clan.
Upon taking the reins of power in 1582, Masamune soon found himself entangled in conflicts with the Ashina, over the defection of several Date retainers, and the traditional rivals of the Date, the Hatakeyama. The wars against these two clans would come to show the great ability and the ruthlessness of the man Masamune. [1]
Having marched south and defeated the Ashina of Aizu in a surprising victory at Hibara, he inflicted a terrible vengeance on the traitors to the clan, putting nearly 800 men of all ages to the sword. News of the massacre soon reached the Ouchi at Obama Castle, causing them to panic and flee. [2]
But his reputation as a warrior without pity came when fighting the forces of Hatakeyama Yoshitsugu, who after failing to negotiate with the young and hot-blooded daimyo, asked his father Terumune to mediate between the two. Yoshitsugu nevertheless kidnapped Date Masamune’s father in a trap. Masamune and his men caught up with them near the Abukuma River.
In the ensuing confrontation, Terumune ordered his son and his men to open fire regardless of his own safety. Without hesitating [3], the men fired at the Hatakeyama party, killing everybody including the Hatakeyama lord and Date Masamune’s own father.
Following the incident, Masamune marched upon Nihonmatsu castle. A few months later, a general war erupted as the Hatakeyama rallied the Ashina, the Satake, the Soma and other clans to fight the Date. The coalition would nevertheless proved to be shortlived, as the Satake would be forced to leave the war in order to defend their own lands from the Satomi, upsetting the balance of power and giving the Date the chance to broke new deals and clear his path to regional hegemony.
When Katsuyori met Masamune on August of 1588, he had subdued the Soma and was in the process of besieging the Ashina headquarters at Kurokawa. By the end of the operation, the Takeda recognized the Date as the main clan of Mutsu, whereas Masamune presented Kurokawa and a over 2,000 enemy heads on pikes as a sign of respect and vassalage.
The conquest of Aizu and the lands of the Hatakeyama, authorized by Katsuyori in the fall of 1588, would put the Date domain at the height of its power; coincidently just as the Takeda themselves were at the pinnacle of their own.
Notes:
1. IOTL, Masamune took over in 1584;
2. IOTL, Masamune was stopped at the Hibara by Iwashiro Morinuki, not present ITTL;
3. IOTL, two versions exist: a. Masamune hesitated before shooting, and the Hatakeyama lord escaped; b. Masamune did not hesitate, and killed them all...I'm going with version B for ITTL;