Cortes could not have conquered the Aztecs as easily as he could have, without some form of help; specifically, his use of having allies on his side. None of Cortes' history of his conquest would have been fully understood had it not been for one of the men in Cortes' army who wrote it all down, and his name was Bernal Diaz Del Castillo. From the short novel called The Essential Diaz: Selections from The Conquest of New Spain by Bernal Diaz and translated by Janet Burke and Ted Humphrey, relives the troubles and the methodical thinking of Cortes's psyche through the memories and eyes of Bernal Diaz. From evading the oncoming Spaniards to fighting the Aztec army, Cortes' victory on conquering Tenochtitlan could have not been possible without his use of alliances. Some of the importance alliances that he made was with the Cingapacinga and the Cempola in chapter 6, the Tlacaltens, which was mainly chapter 7 and 8, to having Panfilo de Narvaez and Narvaez's army join Cortes on his journey to capturing Tenochtitlan, which was in Chapter 11-14.
One of Cortes' first alliance was with the Cingapacinga and the Cempola, who were both enemies, but united because of a cause. This cause was the Aztecs, who were collecting taxes, and sacrificing people from both groups. Through the Cingapacinga and the Cempola, Cortes learns that most of that cities under Aztec rule was taken by force. Under these conditions, Cortes was able to unite the Cingapacinga, the Cempola and the neighboring city Totnoc under a cause, which was to get rid of the Aztecs. The Cempola, and probably the other two also, gave Cortes warriors to accompany him on his trip.
In Chapter 7, the Tlaxcalten initially met the oncoming Spaniards with hostility, and the Spaniards would have been all killed because the Tlaxcalten outnumbered the Spaniards, but had it not been for Xicotencatl's father, who persuaded Xicotencatl, who was the Tlaxcalteca's war leader, that it would be wiser to ally with the new and upcoming mysterious group.