In the han system, Obama was a political and economic abstraction based on periodic cadastral surveys and projected agricultural yields. In other words, the domain was defined in terms of kokudaka, not land area. This was different from the feudalism of the West.
The domain's capital of Obama was a prosperous port city throughout much of the 15th-17th centuries, though it gradually became a quiet provincial castle town later in the Edo period. Still, it was an important link in the domestic sea routes between Ezo and the Sea of Japan coast, and played a significant role in the economic development of the early Edo period.
In the Sengoku period, Obama was controlled by a succession of lords, including members of the Takeda clan, followed by Niwa Nagashige, Asano Nagamasa, and others, including Kinoshita Katsutoshi. In 1600, Kinoshita did not participate in the decisive battle of Sekigahara in 1600, but he was deprived of Obama because he had not actively supported the winning side.
In 1600, Kyōgoku Takatsugu was established at Obama. In part, this was a reward for his leadership during the Siege of Ōtsu. In the same week as the Battle of Sekigahara, Takatsugu did fail to hold the Castle of Ōtsu; but the outcome at Sekigahara marginalized any adverse consequences of his defeat. In moving Takatsugu to Obama, the shogunate effectively acknowledged that Tadatsugu role in the victory at Sekigahara was critical. The siege siphoned men away from the massed array of forces the Tokugawa faced at Sekigahara. In other words, this meant that the attackers at Ōtsu were unavailable to augment the anti-Tokugawa fighters at Sekigahara.
In 1607, Tadatsugu's son Tadataka was married to the fourth daughter of Shogun Hidetada. Two years later, Tadataka became daimyo when his father died in 1609. Tadataka would remain at Obama until 1634; and then the bafuku ordered him to move to Matsue Domain in Izumo Province.
Sakai Tadakatsu, formerly of the Sakai clan at Kawagoe Domain in Musashi Province, then became lord of Obama. Sakai was one of the shogunate's top officials, serving on the rōjū council, and later as its head, or Tairō. He was succeeded in the domain by his fourth son, Sakai Tadanao.
Tadanao distributed out parts of his income to create new domains. The 10,000 koku domain of Katsuyama in Awa Province was thus established for his nephew in 1668, and the 10,000 koku domain of Tsuruga in Echizen Province was created in 1682 by his son. After another 3000 koku was given to Tadanao's fifth son Sakai Tadane, the domain was reduced to 103,500 koku.