American soldiers, including many West Pointers, have…

American soldiers, including many West Pointers, have never engaged in urban warfare and they march straight down the open streets, where they are annihilated by Mexican defenders well-hidden in Monterrey's thick adobe homes.

After two days, they change their urban warfare tactics.

Texan soldiers have fought in a Mexican city before (the Siege of Béxar in December 1835) and advise Taylor's generals that the Americans need  to "mouse hole" through the city's homes.

In other words, they need to punch holes in the side or roofs of the homes and fight hand to hand inside the structures.

Mexicans call the Texas soldiers the Diabólicos Tejanos (the Devil Texans).

This method proves successful.

Eventually, these actions drive and trap Ampudia's men into the city's central plaza, where howitzer shelling forces Ampudia to negotiate a truce.

Taylor agrees to allow the Mexican Army to evacuate and to an eight-week armistice in return for the surrender of the city.