Yes, but even if they didn't surrender, there are other ways to deal with this besides slaughtering an entire population.

This included biological warfare of throwing infected bodies over the walls of cities.

The Mongols also were curious about religions and customs, and sometimes they adopted those ideas for themselves.

Nasir Al-Din Al-Tusi married a Mongol and was then put in charge of the ministry of religious bequests.

Nasir Al-Din Al-Tusi convinced Hūlāgū to found an astronomical observatory and he oversaw the construction of this major scientific institution and its instruments in Marāgha, the Mongol headquarters in Azerbaijan, and he became its first director until his death in 1274.

Nasir Al-Din Al-Tusi was asked to become the Mongols scientific advisor when they came to his village.

When the Mongols were conquered cities, they killed or enslaved anyone who didn't submit to them.

Many Mongol nobles died young of drunkenness which isn't very civilized.

When a Mongol army ran out of food, they ate one of every ten of its own soldiers.

After the Mongols took control of most of Eurasia, they protected the silk roads making them thrive with trade.