Even though you brought wealth to your empire you destroyed many cities and murdered a lot of peaceful people.

Did they allow Prince Mstislav lll of Kiev to surrender, since they always asked a state if they were willing to surrender peacefully?

After their defeat the Mongols decided to try and invade Japan for the second time which caused even more soldiers and people on both sides to die.-Hojo Tokimune

Mongols didn't let the people that carried the letters return without an answer from Hojo Tokimune, therefore they were killed.

When invading Japan for the first time many Mongols died in the typhoon, however they refused to surrender at first.-Hojo Tokimune

When invading a state that reused to surrender mongols wouldn't destroy the art.

Before invading a state they let the people surrender. If the did the Mongols wouldn't kill anybody, and only if they refused to surrender the Mongols would start killing them.

They rebuild and protected the Silk Roads, therefore many merchants started trading again, which increased trade and improved the economy in many states, in Asia, Africa and Europe.

Mongols enslaved people that were able to do something that Mongols couldn't.

Mongols murdered entire cities that refused to surrender.