The cultivation of maize allowed for the development of Tenochtitlan because it created a staple crop that all citizens can grow. Growing crops is an essential part of any society, as it provides food which individuals/families can live off. Without this staple crop, this group of Aztecs would need to have a more nomadic lifestyle in which they constantly moved to hunt animals.
Tenochtitlan was vulnerable to conquest because it was surrounded by water. Being surrounded by water made it easily accesible to other countries. This is why Spain was able to invade and take over Tenochtitlan during the 16th century.