He sided with the Western army, supported Ishida Mitsunari during the Sekigahara Campaign and had evidently plotted to assassinate Tokugawa Ieyasu beforehand.
His brother Maeda Toshinaga sided with the Eastern army of Tokugawa Ieyasu.
After Mitsunari's defeat, Toshimasa was forced to retreat and surrender his lands to his older brother, Toshinaga.
Due to his mother's appeals, Toshimasa was saved from execution and later he was confined to Kyoto and became a monk.
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