generate questions: In 1226, immediately after returning from the west, Genghis Khan began a retaliatory attack on the Tanguts. His armies quickly took Heisui, Ganzhou, and Suzhou (not the Suzhou in Jiangsu province), and in the autumn he took Xiliang-fu[disambiguation needed]. One of the Tangut generals challenged the Mongols to a battle near Helan Mountains but was defeated. In November, Genghis laid siege to the Tangut city Lingzhou and crossed the Yellow River, defeating the Tangut relief army. According to legend, it was here that Genghis Khan reportedly saw a line of five stars arranged in the sky and interpreted it as an omen of his victory.
In which year did Genghis Khan strike against the Tanguts? {sep_token} What season was it when Genghis Khan took Xiliang-fu from the Tanguts? {sep_token} Who won the battle near the Helan mountains? {sep_token} What river did Genghis Khan cross before defeating the main Tangut army? {sep_token} What omen was Genghis Khan reported to have seen assuring his coming victory against the Tanguts?