Write a question about the following article: The Kaga Rebellion or Chōkyō Uprising was a large-scale revolt in Kaga Province , Japan, in late 1487 through 1488. Togashi Masachika, who ruled Kaga Province as shugo, had been restored to power in 1473 with aid from the Asakura clan as well as the Ikkō-ikki, a loose collection of lesser nobility, monks, and farmers. By 1474, however, the Ikkō-ikki grew discontent with Masachika, and launched some initial revolts, which were easily quelled. In 1487, when Masachika left on a military campaign, between one hundred thousand and two hundred thousand Ikkō-ikki revolted. Masachika returned with his army, but the Ikkō-ikki, backed by several disaffected vassal families, overwhelmed his army and surrounded him in his palace, where he committed seppuku. The former vassals of Masachika granted the position of shugo to Masachika's uncle Yasutaka, but over the next several decades, the Ikkō-ikki increased their political hold on the province, which they would effectively control for almost a century.

Question about the article:
How many decades passed when Ikkō-ikki increased their political hold on the province?