The correct answer to this open question is the following.
Unfortunately, you forgot to include the information about page 13, or the excerpt of the text so we could know what is this about. We do not know what was n page 13, just you know it.
However, trying to help you we can comment based on our knowledge of this topic.
The Tlaxcalan leaders joined the Spanish conquistadors. What this suggests about the relationship between the Tlaxcalans and the Aztecs was that teh Tlaxcalans were enemies of teh Aztecs.
And this is correct because the Aztecs were great warriors that wage war and took prisoners. The Great Aztec Empire was a dominant one, and force other Mesoamerican Indian tribes to pay tribute. So we can say that those other small tribes or less powerful tribes had to pay tribute if they wanted to be on peaceful terms with the Aztecs.
That is why the Tlaxcalans and other tribes such as teh Chilollans decide to join forces with Hernan Cortés and teh Spanish conquerors. Together, they showed strong opposition to the Aztecas. And that was a good advantage, considered that the Spanish conquerors had horses, spades, blades, and fire weapons that impressed the Native Indians.
