The Aztec had a huge army. Most of them were freemen, or commoners, and a few were professional soldiers who were nobles.
Just like Rome, the Aztec Empire relied on taxes from its growing empire, so warfare was important. If you were a commoner and wanted to get on in life, the only way was to show greatness as a soldier, and you did this by taking captives. Captives were then used for sacrifices. War and religion went together.
