About Battle Of Sekigahara 21 October 1600 Part.2

Heavily outnumbered, Otani had no choice but to retreat. This left the Western Army’s right flank wide open, so Fukushima and Kobayakawa began to roll up it. Thus Ishida’s right flank was destroyed and his center was being pushed back, so he decided to retreat.

Ishida’s only remaining forces were on Mount Nangu. However, these forces were there for a reason. Kikkawa Hiroie was one of the commanders on the mountain. Kikkawa's troops formed the front lines of the Mori army, which was commanded by his cousin Mori Hidemoto. Earlier, when Hidemoto decided to attack the Tokugawa forces, Hiroie refused to comply, stating he was busy eating and asked to be left alone. This in turn prevented the Chosokabe army, which deployed behind the Mori clan, from attacking. When Ishida arrived, Kikkawa betrayed him as well. He kept the Mori army at bay, and since Ishida had no more support, he was defeated.

The Western Army disintegrated afterwards, and the commanders scattered and fled. Some, like Ukita Hideie managed to escape, at least initially. Many others did not. Shima Sakon was shot and fatally wounded by a round from an arquebus and Ōtani Yoshitsugu committed suicide. Mitsunari, Yukinaga and Ekei were some of those who were captured and a few, like Mōri Terumoto and Shimazu Yoshihiro were able to return to their home provinces. Mitsunari himself would be executed.

Both sides had forces that did not arrive at Sekigahara in time to participate due to other battles.

Ieyasu's son Hidetada led another group through Nakasendō. However, Hidetada's forces were bogged down as he attempted to besiege Sanada Masayuki's Ueda Castle against his father's direct orders. Even though the Tokugawa forces numbered some 38,000, an overwhelming advantage over the Sanada's mere 2,000, they were still unable to capture the strategist's well-defended position.

At the same time, 15,000 Toyotomi troops were being held up by 500 troops under Hosokawa Yusai at Tanabe Castle in present day Maizuru, Kyoto Prefecture. Some among the 15,000 troops respected Hosokawa so much they intentionally slowed their pace. Due to these incidents, a large number of Tokugawa- and Toyotomi-aligned troops failed to show up in time for the battle. Had either of these armies participated in the conflict, it could have ended quite differently.
Source: Wikipedia