Though they technically bordered each other, the Mongol and Khwarezm Empires touched far away from the homeland of each nation. In between them was a series of treacherous mountain ranges that the invader would have to cross. This aspect is often overlooked in this campaign, yet it was a critical reason why the Mongols were able to create a dominating position. The Khwarezm Shah and his advisers assumed that the Mongols would invade through the Dzungarian Gate, the natural mountain pass in between their (now conquered) Khara-Khitai and Khwarezm Empires. One option for the Khwarezm defense was to advance beyond the towns of the Syr Darya and block the Dzungarian Gate with an army, since it would take Genghis many months to gather his army in Mongolia and advance through the pass after winter had passed. The Khwarezm decision makers believed they would have time to further refine their strategy, but the Khan had struck first.