The contrast between Genghiz Khan and Alauddin Muhammed was as marked as it ever was between two generals who have squared off against each other. Genghiz was a warrior, cruel, merciless, relentless, master of deception but who led his armies with the skill becoming of a great conqueror. Alauddin, by contrast was lacking in skills both of tactics and strategy and was a coward who fled with his own men without giving battle. Genghiz always gathered intelligence about his adversaries before combat.

Alauddin knew nothing of his mortal enemy but provoked him into war. This was a civilizational encounter wherein the Mongols had the advantage of technology, skills, intelligence, tactics and leadership. The Sultan, by contrast, demonstrated a fatalistic self-delusion and knew nothing of the technologies, skills, tactics, motivation or capabilities of his enemies.

Genghiz followed up his assault on one city after another. In the year 1219 the cities of Otrar, Jhand, Khokand, Bukhara, Samarqand and Signac fell one after the other. In each city the pattern was similar. Men, women and children were slaughtered except those needed as slaves for work during the military campaigns. Agricultural land was turned into grazing ground for Mongol horses and the cities were razed to the ground.

Dams were destroyed, libraries burned, mosques demolished and learned men tortured to death. Shah Alauddin Muhammed fled before the Mongols and was hunted from city to city. During the year 1220, Balkh, Nishapur, Ghazna as well as the provinces of Kuchan, Isfahan and Damgan fell. The Shah finally escaped to an island in the Caspian Sea where he died a pauper, leaving a legacy of cowardice rarely matched in Islamic history.

source:

https://historyofislam.com/contents/the-post-mongol-period/genghiz-khan/

http://97.105.52.213/en/artical/21413/Contrast-between-Genghiz-Alauddin