The source is from the database that the school provided, the same one where you also probably got your evidence from and it was never specified in the article as to how it was documented.

Was there anything in specific that Marco Polo was impressed by with how the Mongols lived or was he just impressed with the general way that they lived their day-to-day lives?

Prince Mstislav lll of Kiev - The Mongols then stripped Mstisav of his power, as the Mongols took over the land that Mstislav ruled over.

Prince Mstislav lll of Kiev - The Mongols only left 1 out of 10 soldiers in Mstislav's army escape including Mstislav. The rest were either killed or used as human supporters for furniture for the party used to celebrate the Mongols winning the battle.

Prince Mstislav lll of Kiev - Mstislav was the prince of a large portion of Russia and he also fought against the Mongols when hearing news that they would be invading Russia.

The Mongol Empire was one of the main reasons for the Bubonic Plague spreading across such a large area.

People from conquered lands that were deemed useful to the Mongols were forced to do work for the Mongols without that person's consent.

The Mongols massacred entire cities without mercy during their conquest to power.

The Mongols practiced religious tolerance, which allowed the people of the Mongol Empire to not live in fear because of their identity.

The Mongol Empire created a connection between Europe and Asia, which was the first time that the two had ever been connected.